I don't see a way of distinguishing between bad behaviour and discussing taboo topics. They're so often the same thing - consider flat out racism or misogyny for example. An things get even more complicated when you consider /b/-like levels of irony and inversion of meaning, where it;s difficult to tell what is a incredibly subtle troll of racists, and what is actual racism.

But I'm glad that the whole internet isn't /b/. I'm glad that terrible perspectives are often shunned from conversations. It's good to remember they're there, but if someone comes along and expresses terrible things then they should feel shame. And that only happens if those perspectives are not welcome, and are made to feel not welcome.