The Character Romance thread (Official)

He did not blow the Chantry up because he's a mage. He blew up, because the mages were under oppression. This is different. Anders' didn't want to rule over anything. Fenris fear from the oppression too. He was happy at the mage side finally...

What power? The power of black powder/lyrium bomb?
"Blaming magic Isn't the answer..." – Hawke to Fenris, friendship.

Rivalry: After the Alone quest he doesn't blame the magic/mages anymore. In romance as a mage Hawke, this is good point.
If Fenris try to left Hawke (not enough friendship/rivalry), Hawke can convince him with "I assumed, that the freedom from slavery means something to you" – or something similar, and Fenris leave Meredith and join to fight for mages...
Non-romanced Fenris after Alone (friendship is very good!)

Especially when you consider that it also could have just as easily been Nathaniel or Velana.

Fenris is free of slavery (for now?) and now his feelings and experiences aren't valid and important?

Nathaniel? For what? 
Anders more interesting with Justice. Nathaniel and Velanna never were considered as "funny" dudes, Anders was. (Of course, he never was "funny", but the people saw him as funny.)
Nathaniel and Velanna was grumpy in Awakening. I do not think the players would have noticed any change in them with Justice...

But Anders spectacularly changed (not really, just spectacularly – according to my opinion). Many people see, that Anders spoiled by Justice, because he's not that a nice guy, who was before Justice, in fact, sometimes became a jerk. "Justice don't let him be happy"... or (as I see): he already doesn't care about what people think about him, and he doesn't have to hide behind a charming, "funny" guy? What about, if he simply tired of being a charming funny guy?

He also know, that there are "noble people" among the Magisters as well (Gallows, Act 1), so not all mages are evil tyrant. In fact, at the moment Meredith is the evil tyrant. 
He supports the Circles not from ideological conviction, rather from fear. His fear is understandable, because his master was a mage. But his fear's not logical, because his master was a slaveholder, who was a mage. He able to understand that difference. He lives in Southern Thedas already at least for 8-9 years, in Kirkwall for 7 years. He able to recognize, that's not Tevinter. I know, this is hard. This is his trial. And he still can support the Templars. 

The point is, Fenris does not give up his conviction. After the Alone, he already able to leave his fear behind, and without or with doubts (depend on Hawke's behavior toward him), he able to fight at mage side, not for the Mages, rather for his friends.

(By the way: as I remember, my Hawke's ask was: "so hard to you to die with your friends?", instead the slavery version)

I'm not sure if his disdain towards mages is illogical. I mean, by your words, his master was a slaveholder, who was was a mage. I'm sure there's a logical reason why Fenris would fear mages, instead of slaveholders/as well as slaveholders. But I'm not good with DA lore so I'll drop it. It's been a year since I touched DA2 to begin with. Don't really like to imagine that everyone's fear or disdain of magic and mages is unfounded and illogical. Unless that's what BW wants to do, paint magic and mages as perfectly fine cinnamon buns that does no wrong, who do no wrong. I don't like that.

It's easy to me, I recently finished a two playthrough (both friendship with him: romance and non-romance). 
You have a point: of course, his fear has logical basis, if we speak about that the magic/mages are dangerous, and his master was a power-hungry blood mage. The illogical part of this is the "mages", and he knows that very well.
I can say: the caution is logical, the fear is rather illogical. The last friendship romance with him was a challenge/try with radical pro-mage. Hawke took him everywhere, and was totally honest with him about his conviction. So truly this was a (soft) rivalry, but still: working. He's rather a good person than anti-mage (he's anti-slavery, and on this way, Hawke can help him any time).

No one deny the danger, but the "prevention" method is bad and cruel. This is why I support Anders. (Who isn't perfect, nor even innocent – but hot.)

plus, DA2 Anders was different that DAA Anders because of Justice merging with him. Of course Anders is going to change, since he is sharing his body and consciousness with a spirit.

I like to make a hardened Leliana Divine in my Lavellan PTs as a way of trying to undermine the Chantry. It really bothers me that while they give you a few dialogue options here and there to say you aren't Andrastian, the game always assumes you want to help fix the Chantry while you are saving the world. I would have like for there to be a path where you take control of the Inquisition to oppose the Chantry. So if I can't have that, I pick a Divine who might destroy it from within. (all this is of course my headcanon, I know none of it will ever matter in any future game.)

Just everything you said is spot on. Bless you! 

Especially the last bit about not killing Anders. Yeah Anders, this is the war you wanted, well here you go, now watch and enjoy the blood spill forth! 

Er, no. Meredith and Elthina did not rain a giant stone building down on a densely populated city. That decision was made by Anders. Certainly there is a lot to be said for Meredith's general blame in the story, but I'm sorry, Anders is not getting absolved for the murders he has willingly committed. I get agreeing with him, arguing that it really was necessary to force the cathartic mage/templar confrontation to avoid greater problems in the future (which I don't at all, but I see the argument), but he is a murderer of innocent people. I don't think even he would disagree. (Edit: I forgot to mention, he also explicitly states he wants this general conflict escalated, which I'm sure Meredith also does, but her being a bad person doesn't make Anders a better one.)

Also, Varric is not pro-templar, he is actually one of the companions in the game who doesn't give you any pro or con points merely for choosing either side. Instead he disapproves and approves on the basis of how unnecessarily cruel you are. I don't think Varric works as proof here, anyway. The whole plot of DA2 is basically about Templars under Meredith growing ever more cruel towards the mages. Tranquility is a continuing concept throughout the series that no sane person can agree with, the treatment of the Qunari mages is brutal to a point of absurdity, and we hear many tales of mages being abused and oppressed in the Circles. There are sympathetic Templars, too, but on a whole I don't feel the DA world really wants to bring home the idea that the Circles are good and the Templars are generally right the way they operate during DA:O and DA2.