Without rules, people do whatever they want. Toady keeps the rules loose but sharp, like a whip, which is why Bay12ers have some manners. Those who discarded their manners, like Yanlin, were kicked out even though they contributed to the discussion.
My best friend is an Internet troll who spams people on Facebook, goes to gay chat rooms to tell them how much he hates gays, posts on fan sites of R&B stars to call someone a "filthy nigger". He's a great, nice guy in person, but on the Internet, he's a bit extreme. He does stop after a 3-day ban.
Best solution: enforcement.
Dasleah did a perfect imitation of an Internet asshole. They're assholes not because they want to be rude. They're asses because they think it's funny. I'm sure 90% of the rude /b/tards think it's funny. It's the same type of funny when you run up to someone as a kid, poke him in the butt with a stick, then run away. It's against norms, it's unexpected.
"your drawing sucks, you should give up on art" or "you should be banned for being a girl" is something that's so stupid it should come up as sarcasm. And sarcasm is supposed to be funny. But with some insecurity, it's seen as an insult and completely rude. The worst thing about the Internet is that without smileys, you miss out the tone. A black guy making fun of a black guy on Comedy Central is obviously a joke. A black guy (assuming you even know he's black) making fun of a black guy on the Internet is a bannable offense.