I used to get hooked on a lot of TV shows, and then get disappointed with them, and I eventually came to the conclusion that you can't trust fictional characters. No matter how good and consistent they seem at the beginning, they're always going to end up doing something stupid and out of character, possibly something hostile, that you were certain they would never do. At least that's the impression I got from TV. And it always turns me off from the show. I get into a TV show or a book because I like the characters, because I feel like I can trust them. So when they break that trust, it's like the whole point of why I liked it in the first place is gone.
I know sometimes this happens and it's not the fault of the character. Like, in a supernatural universe, sometimes there's some mystical device that causes a character to become evil in some way, or otherwise out of character. Red kryptonite, for instance. I can forgive the characters for things like that, but I still don't like it. If I'm interested in a piece of fiction because of the characters, I don't want to see the characters being forced to not be themselves by some mystical power. I don't think it's fair.
This is one reason why I wanted to start my own work of fiction with my own characters. There are a lot of things about my comic that I don't take very seriously, but what I do take seriously is the integrity of the characters. It's not like the characters are all completely moral and trustworthy, but they all have their own kind of integrity, and you can trust them all in certain ways. I care so much about the integrity of the characters that I'm not going to make them do anything that goes against that.