This is the thing that has baffled me most.

The joker doing something that might be immoral to a super hero is considered wrong to portray.

But the joker, is a villain. By definition, his actions are immoral, and he inflicts said actions against people who do not deserve it, such as bat girl here.

This is like when the religious right try to ban tv shows or games, because bad guys do bad things to people in them.

But muh victimhood!