What if this was about black people right to sit at the front of the bus? Would you still say: "Why do you want to share your opinions on controversial topics? What do you get out of it? No one cares about your opinions on apartheid except to dunk on you. You're not going to revolutionize society's opinions on black people. So stop doing that."

Not saying incest and apartheid are the same thing, but we need to be able to discuss all ideas in an open way, even the ones that most of us find uncomfortable. Otherwise democracy dies.