You can do that, or at least you can save Ferelden and install yourself
as a king or queen. In fact you can determine *two* kings, both of
which for the sole reason that they'll help you do something you want
to do. But you can't do that by ignoring other people's needs, you
still need to do one or two things that might be considered good on a
smaller scale.
Being a King/Queen is not an option for some origins. You have to pick a ruler regardless. I much rather the human empire fall and humanity suffer. Use them to defeat the darkspawn then have them civil war to death. It is not an option at all for the Dalish to give the finger to humanity. Everything in the Dalish background has them tolerating to hating humans yet when giving the chance to screw them you cannot.
The thing is you don't get to choose between good or evil. Evil is as
much defined by your intentions as it is by your actions. You can kill
Connor because you like killing children and it's evil, you can kill
him because it's the only way you see to banish the demon and it's
good. You can save Isolde and Connor both because you really like them
and it's good, you can save them both because you want the Arl's
political support to overthrow the queen and the regent and it's evil.
I rather kill Connor because he is a human and it's the path of least resistance. The dialogue doesn't allow my intentions to show as evil. It does however clearly on numerous occasions allow for good intentions. "I won't harm an innocent" is used how many times? Killing him is a greater good option for safety. I rather wipe out the Arl's family, be the only one to tell him what happen, get his help then let him fight Logain. Again good intentions are clearly expressed throughout Dragon Age but evil intention is rare and often is just being an ass.
So the assassin that used her seduction talents to solve conflicts with
"less violence" is pure good? Suuure. The desire demons must be good
too then? They do the same thing. And Wynne has her own little secret
that she puts a lot of effort into making it look like it's not so bad
at all. I'll give you that Alistair isn't evil, but he's too
small-minded for any grand evil overlord ambitions anyway.
Throughout the game you so much as fart in a hostile manner to someone, Leliana disapproves. Don't give aid, disapprove. Don't be nice, disapprove. She completely regrets her past and is trying to make up for it. She is pure good now with chaotic good in the past. Still clearly good. Wynne is exactly the same. They have different sins in the past but as far as playing the game it's girl scouts all the way.
Morrigan isn't evil at all. She doesn't trust anyone and conversely has
no need to go out of her way to help anyone, but if you'd leave her on
her own she'd not go on a rampage for silly reasons. Like Sten...
I've had Morrigan in party 100% of the time it's allowed. Her banter shows she enjoys the suffering of others. Yes she is in it for herself. Often her dialogue goes beyond "I don't want to help" to "they deserve to suffer." She takes pleasure in it. Rampages does not make an evil person. Serial killers don't go on rampages. Sten is suffering greatly for killing the farmers. Evil people wouldn't have pain from doing it.
Actually that line is from Morrigan ("Power has meaning. Survival has
meaning."). Zevran will turn on you (and die for it) if he doesn't like
you.
Only because he fears the Crows more than you. He'd be with the Archdemon if he thought he'd survive. He is not really true evil in that he is plays on whatever side he thinks will win. Morrigan is interested in power and is willing to die if she can't have it.
The amount of content in quests and dialogue in story developement is schuing heavily on the side of good. Evil comes off as being a social misfit.