> They say we have freedom of expression. Why do I have to be careful of the art I create?

Freedom of expression doesn't mean you shouldn't be responsible of what you create.

> If I want to draw 10,000 lolis being raped and torn apart by monsters or something, what's the problem?

It is obscene.

> Is that seriously comparable to actual child pornography??

No, but how would you explain that to people who just want to protect the children?