So why does almost everyone wo supports a canon ending want Destroy to be canonized?

No she didn't they specifically state they have food for Turian and Quarian to eat.  Zaeed if there even mentions he saved you a couple of slices of bacon. Though they still have the some of the dextro based shit in the freezer.  And if you take Garrus with you on the Dreadnought mission he will mention to Tali that he got some dextro chocolate he is willing to share with Tali.  A conversation with EDI post  Tuchunka will take about the logistics of shipping the Krogan off to the front line on Palivan. One of the thing she mentions is how the food of Krogan and Turian are incompatible. Requiring the Krogan to carry their own food supplies.

video?

I assume you mean this video:



The one were Tali panics at the end.  Course you can also talk to her afterwards and say she will just sit there quietly and wait for someone to change the subject 29:44-30:32 has Tali out right saying that she practically poisoned her self with cheese in an attempt to change the subject.

So yea she ate it but only to change the subject of what was being talked about and had to do some damage control from eating it to prevent herself from being poisoned. In a manner of speaking.

'Destroy' was the whole goal of the first 3 games, up until you suddenly had a choice at the very end. I'd pick 'Destroy' as canon only because I didn't feel the other two made sense from the context of the rest of the games. But, since they give options, it nullifies any canon ending really.

I'll say it again: if Shep died w/ a heroic death w/ Anderson at the end of ME3 and Reapers were destroyed - with no choice involved - I'd been so happy.

I'm going to call this my favorite reason not to choose this option.

As one of those guys who insist "Destroy" is the ending that should be canonized, I can explain why.

It's Shepard's decision
For 99% of the game Shepard's goal was to end the Reaper threat by destroying them. S/he saw two of three alternatives over the course of the trilogy as well, namely:
SYNTHESIS - that's what Saren was after. He believed he could make sentient organic beings useful to the Reapers, so they'd integrate them into their plans. Also he believed the only way to become useful to the machines is to become part machine, taking the "best of two worlds". Obviously he didn't think things through, since the Reapers weren't interested in such trade. However, Souvereign found Saren quite useful and gave him what he wanted - the hope of surviving the upcoming Reaper invasion somehow. We all know Saren was indoctrinated.

CONTROL - that's the trade of TIM. He wanted to control the Reapers for the better of mankind. Well, we all know power corrupts and absolute power corrupts absolutely. Who should be allowed to hold such terrible power at his disposal? TIM? Any other human being? Shepard? No. Besides that, TIM nowhere was close to actively control the Reapers. All he'd achieved was limited control over ground forces of the Reapers, but not a single Reaper itself. And, of course, TIM was indoctrinated as well, so the Reapers simply gave him the illusion he could control them, while they were well aware he could never achieve that goal.

Both endings, Control and Synthesis, are more or less based on indoctrinated thoughts. Saren thought he could make himself (and organic beings in general) useful for the Reapers by willingly become "closer" to them, yet he was indoctrinated to believe so. We all know what had happened to the Protheans that turned into Collectors: no culture, no own thoughts, no soul - everything replaced by tech. That's no existence ANY sapient being wants to suffer.
And TIM though he could control the Reapers, because he was indoctrinated to believe so. Of course, how can a single mind (even a rather resourceful one) can even think of controlling billion year old AI beings? That's all part of their strategy; TIM could have used his resources researching strategies, tactics and techs to engage war against the Reapers. Instead he wasted all of his resources on research how to control a couple of husks.

So Shepard had a chance to see two other alternatives to his/her own goal. And, well at least in my mind, s/he wouldn't go after them because they were both pursued by indoctrinated persons.

"Dead Reapers is how we end this war" is what Hackett said
Shepard is a Spectre, but that doesn't mean s/he's no longer loyal towards the Alliance military. At least the Paragon!Shepard is still following orders, even if s/he hasn't to do so. So when Shepard is deciding for "destruction of the Reapers", s/he's more or less following Hackett's orders, that is.
Of course, Paragon!Shepard isn't Canon!Shepard - there isn't any. But I bet even a full Renegade!Shepard will decide for destruction of the Reapers, because s/he'll finish the job, no matter the cost. In a twisted way, Renegade!Shepard may be way more alligned towards "Destruction" than Paragon!Shepard that may have second thoughts about genocide of an entire species (which, tbh, the Reapers are).

Space Magic
Nobody likes that word. Out of the three options, "Synthesis" is the one that simply feels like "space magic". Shepard simply decided for trillions to turn them into hybrid beings. Although I'm a supporter of transhumanism, I believe that decision should be made on an individual basis. No one should decide for everyone else something like that.
The "magic" part kicks in after releasing that green wave. Whatever is happening, it'll turn organic beings into hybrids - which can be explained by usage of "nanites", similar to those used by the Borg (Star Trek). But how the heck does it work the other way around? How do synthetic beings end up being part organic?
Also there's that uneasy idea about husks, banshees and brutes turning into actual people. They got maimed, altered, cut into pieces and reassembled against their will and now have to live with what they have become. Out of the three named before, husks are the more lucky ones - they're not entirely abominations. What about brutes? Oh, and then we still have the Cannibals. Not sure if those former Batarians like their new appearance.
Even "space magic" won't make those ugly implications go away.
And: if one opted for ending the Morning War in a peaceful manner (Geth and Quarians survive), there's no need to fuse organics and synthetics into one: the foundation for deep understanding between both sides is set and simply needs time to develop. The Catalyst's flawed logic, synthetics had to destroy organics to prevent synthetics destroying ALL organics, is utterly vanquished by that particular event. Organics and synthetics can live in peace, they just need to understand each other.

Control in the other hand is no true "space magic". It's simply moving control from one entity to another. AI!Shepard is based on Shepard's thought patterns, which is a bit space magic, but not much more than Shepard's revival via Lazarus project. So no "space magic" here. Also "Control" is the only other ending I might accept as canon insofar, as Shepard is moving the Reapers to some spot in the galaxy they don't bother anyone. Making them guardians of the galaxy may sound like a good idea, but how much freedom do people have in a heavily watched galaxy? I don't want some incredibly powerful beings watching over me, that's for sure. Also there's no chance AI!Shepard won't change over time. Today s/he's the ultimate guardian, protector of the galaxy and everything else, tomorrow s/he may suffer the same flawed logic the Catalyst experienced, resulting in continuation of the cycle. And I'm not even speaking about "absolute power corrupts absolutely" (mentioned earlier 'though).

That being said, if Bioware is ever going to canonize one of the three (four, including refusal) endings, "Destruction" has a very high chance to be picked. "Control" is the second one, if they want to bring back the Reapers. "Synthesis" in the other hand sounds like something that won't be picked, mostly because BW had to deal with the husks, brutes and everything else named above.
Also it shouldn't be too hard to bring back the Geth even after "Destruction", or save EDI somehow.

However, the one ending that actually leaves the Mass Effect universe "the most similar to the Mass Effect universe as we knew it before ME3" is Refusal because it even leaves the Reaper War in progress... a war that by the Prothean accounts would likely continue to wage on for centuries.  Destroy not only destroys the reapers, it destroys the geth and affects any other AI technology in the ME universe.  It would tromp on any decision a player may have made to preserve the geth earlier in the game.  It also destroys, if we take the Catalyst at face value, any cybernetics in use because the Catalyst indicates that even Shepard is partly synthetic... but most assuredly, Shepard is not the only one using cybernetic implants.  In fact all those tech upgrades we got in ME2 are labeled as "cybernetic upgrades."  You also have differing levels of destruction depending on the player's EMS.

With such widespread and varying effects, the ME Universe, post-destroy, could be as different from the original as control would make it or even as synthesis would make it (depending on how you interpret it).

I absolutely agree though with your final conclusion... Bioware should NEVER declare any current ending of the ME3 canon.  If they do want to set a story in the post-ME3 Milky Way, they should write a totally new ending totally from out of left field... i.e. presenting a post-war Milky Way that no one who played ME3 could have selected or even imagined.

Yeah, but... eww.

I don't see refusal that way.  The way I see refusal is recognizing that, just as much as using the Citadel without knowing the tech thoroughly was a mistake made by the Asari, using the Cruicible without knowing what it really does and without really knowing how the plans got started and who started them could easily be as much of a trap... further evidenced by the fact that the enemy (i.e. the Catalyst) is now trying to convince you to use it and doesn't seem to really care in which way you do use it.  That is, it isn't trying to actually stop you from using the Destroy option..  A logical conclusion would be that activating it in any way could be the trap that ends the current cycle quickly.  For all you really know, the previous cycles did eventually complete it in each cycle and triggering it is what ultimately completed the harvest and ended the cycle.

On the other hand, you do know that it took the Reapers centuries to harvest the Protheans and that the Protheans actually managed to get a survivor into the next cycle using stasis.  Shepard refusing just means the harvest continues... and it may also take centuries to complete... which doesn't necessarily preclude the current species from eventually finding their own way to defeat the Reapers during those centuries.  It doesn't instantly murder anyone and it could just as easily buy the time needed to really solve the problem without relying on "found tech" that isn't really understood.

No, he's not actively trying very hard to stop you from using it.  He merely tells you what it does.  If he really wanted you not to use it, he could instead tell you it's just the self destruct that won't do anything to stop the Reapers and that your only choices are to insert yourself as the new dictator or broker a synthesis with them.

If you feel he's trying to trick Shepard with Control when he says that Shepard would be able to do things as he sees fit (which might include just having the Reapers stop firing back and sitting back watching them get destroyed by the Alliance), then why would you think that he couldn't lie to simply not tell you about what the destroy option does or that he might not actually try lying in order to coerce you into choosing that one when it might do something far more advantageous for the Reapers.  If the bottom line here is that what the Catalyst says cannot be taken at face value and trusted... then why is that players trust the Catalyst to tell them the truth about the Destroy option?... It's an option being presented by the same untrustworthy enemy as the other two.

As I said, Shepard doesn't really know that everyone dies with refusal.  What he knows is that the war could last for centuries... The outcome of that war would ultimately depend on whether or not the various Milky Way species could find another way to defeat the Reapers... and Anderson keeps assuring Shepard "there's always another way."  The after-refuse ending shows Liara's little time capsule being activated... but does that necessarily preclude it being activated by some surviving the the current cycle's harvest?  It doesn't, since she recorded that message and deposited them all over the galaxy long before everyone was dead.

They (the Milky Way species) also pinned their whole civilization and government on a Citadel that we later find out is actually Reaper tech.  Perhaps it is that Shepard, the only organic to have actually talked to the Catalyst, is the only one who throughout several cycles has had the opportunity to identify the Crucible as a Reaper trap... and maybe, just maybe, not tripping the trap and drawing the war out for a few more centuries is actually this cycle's best chance at survival overall.