OP here, and wow, sorry. "Jerk" was probably the wrong word to use. I'll give you that. I was trying to keep the title short, and my concept is a little vague. I'm having trouble putting it in to words. Maybe some of you who are more articulate could help me express my point better (if I can just explain what it is). I think I'm trying to say some variation on the word "negative".
Let me try it this way:
I remember a lot of people lamenting that you couldn't romance Bethany.
All talk of brother/sister stuff aside, I see their point. Why? Because she's not a morally grey figure. She's genuinely kind, and doesn't resort to dark or desperate methods in her attempts to live a normal life. When the Templar come for her, she doesn't cut her self, spraying blood, and turning in to an abomination (She may be the only mage in the game who doesn't do so in that situation). She's at heart a "good" person.
Alistair is loyal and noble, even if a bit of a buffoon. He genuinely does what is right, and abhors unnecessary death. He's kind to those in need, aggressive against those who genuinely deserve it, sad when good people get hurt, and proud of his friends.
Zevran, on the other hand, is not a nice person. He's just nice to YOU (after he fails to KILL you, anyway). He is more than willing to kill someone, and happily. And he doesn't care if they deserve it or not. Sure, you can credit his horrible upbringing that turned him into a monster. But it doesn't change the fact that he IS a monster (even if a well-spoken and friendly one).
I'm not sure if I am getting my thoughts across correctly.
But I DO thoroughly enjoy these romances with the "darker" characters, such as Morrigan and Fenris. But I ALSO enjoy the relationships with more light-hearted characters as well. I just want more variety, I guess.