How many of us genuinely enjoy playing 'evil' characters?

You are absolutely correct. It's for this reason that I labelled such a character 'chaotic jerk'.

But regardless, I have still executed 'non-canon' playthroughs where I did precisely that -- deliberately choosing every worst-possible outcome out of pure, morbid curiosity to see what would happen if I did. Actually quite surprised that more people haven't done the same.

As for writing, the honest answer is I used to do creative writing. I write professionally for a living (though I suspect that doesn't show up very well on these forums based on the long rambling posts I thrash out) but the type of writing that pays my bills is a bloggy/column style of writing and not creative writing or fiction.

Back in Ye Olden Dayes when dinosaurs ruled the earth and I had more spare time to write short stories and fiction, 'getting inside a character's head' wasn't precisely what I was doing. It was more a case of manufacturing a persona and then encasing it into a blank template. I think that 'getting into their head' implies a form of self-referential role-play based upon thinking as the character thinks, formulating belief systems and actions upon a grossly stretched framework of "what would I do?" and then elongating it to also encompass the mores of the character. I consider all characters are entirely separate beings, each with their own discreet behaviour and thought patterns, none of which bear any relation to my own feelings on the matter. Once this template is built and set in motion, the characters effectively write themselves.

Not sure how much sense any of the above makes. It kind-of abstract and hard to explain in detail. 

I just can't do the truly evil playthroughs. I mean wiping out the rachni is something I could never do and while it wasn't exactly evil given the circumstances I could never kill wrex. The closest I ever came was in DA2 so I could side with the anti qunari people.

We only have the queen's word that the rachni were indoctrinated, she could've been lying to save herself. Even still, given how fast rachni breed, conflict over space and resources is inevitable.

It always annoyed me how few Bioware antagonists lie to Paragon players when caught ("I'll be good this time I pinky swear!"), and/or try to take advantage of their naivete. If not enough do in DA4, especially in Tevinter, I will be severely disappointed.

To be fair, you could just play an evil character that likes dogs. Maybe mabari are your weak spot, and you just can't be evil to them. Then, you wreck everyone else's lives with impunity from your conscience!

Yeah I think the most evil thingI've done in DA is helped the dalish kill the werewolves as my current warden did that but given they ewre a dalish elf themselves they felt justified. But generally in DA when m characters do stuff like that they do it moer as a retalitory strike rather than out of malice in their eyes to remind them who's in charge here kind of thing.

Chaotic jerks, sure. Evil...eh. I haven't gotten around to doing full playthroughs of one, though there have been times where I saved and then tested out all the options of a scenario just to see them for myself. But I never considered those 'canon' for my playthroughs, just a (usually horrifying) what-if. I could only manage to exile Alistair and recruit Loghain once before I hit my wall of 'well, that was traumatizing, time to reload and do this right'.

I'm not someone who enjoys dick choices. But this stems from the fact that they seem to be thrown in there for the sole purpose of having a dick choice. Mass Effect 1 was a great example of this, the decisions that seemed more "renegade" were actually just being a jerkass.

I don't mind having harsh choices for the purpose of my mission, but the justification needs to be good. Often, I find, the reward isn't worth it (this also includes getting a bigger reward for the nice guy act), or it doesn't really affect things in the long run. I mean, throwing a knife in the head of some random pub owner is just being an absolute sociopath.

This is like me. I only ruined the sacred ashes once and that was to get the reaver specilization, then I immediatly canceled the game and went back to an older save.

My biggest problem with Mass Effect's morality system is how "gameified" it is; if you want the higher Persuasion Checks, you HAVE to go either 100% Paragon or Renegade exclusively. It doesn't make much sense to me as a Reputation meter either, since you could be interacting with people who know little to nothing about you, in any order. There's no room for nuance, biases or contradictions, or changing your Shepard's mind over time without sacrificing ability scores.

This annoyed me too. It meant you couldn't give nuance to your character. It was the same with the friendship/rivalry metre in DA2. If you didn't have extreme views one way or the other you could end up with companions turning against you just because you hadn't advanced the metre sufficiently to lock them in. It seemed odd that they could be either end of the spectrum and still be loyal but turn against someone who was not a total bigot, even though in every other respect they were exactly the same person.

I never play someone as a total evil jerk because that just seems stupid to me. Really clever evil people don't make it obvious, particularly to those they want to impress to get them on their side. It is why I so liked Saravok as the evil enemy in Baldurs Gate because he had got the leadership of the city on his side, even though he was a terrible person behind the scenes. That is what intelligent schemers do.

This is why I need to have a valid reason why my PC would make a non-heroic choice. Usually I can justify it from a common sense approach, even though the writers would class this a ruthless. Why risk the safety of an entire village by leaving a possessed kid running around with only his mother and bewitched uncle to keep him under control? Why put Alistair on the throne when he wasn't even capable of stepping up and taking leadership of the Grey Wardens in Ferelden? (Which he should have done having been in the organisation longer than me). Why trust Eamon as an adviser when he had been encouraging Cailan to ditch Anora and likely had been behind the marriage alliance with Celene too? Clearly, a better option was for my PC to marry Anora and then rule jointly with her. Why kill Loghain when he could still bring his years of experience to aid the Wardens? (Which was also the recommendation of the senior warden, Riorden). It would also earn Anora's gratitude for being merciful to her father. At the end of DAO, Loghain willingly sacrificed himself as he said that Ferelden would be in good hands with my PC. Some people might not take approbation from Loghain as a compliment but my guy thought it was totally true. Incidentally, he rejected Morrigan's proposal because he didn't trust her but gave Loghain the option first and Loghain begged him not to make him sleep with her. Did his choices make him evil? Some might say so but I saw it just that he was a pragmatist and adept politician. I did play him differently to how I normally would and how I played my other Wardens but he wasn't making certain decisions without me having a valid reason why he might do so.  He also did have some moral principles.   For example, he would never do a deal with the slaver, although he gave him the option to walk away with his life but the slaver wasn't wise enough to take it.