The topics are definitely fringe but I'm sure you could find some forum or site that discusses it but I think you have things backwards. It's not that most people wouldn't dare to talk about these ideas in polite company. It's that the people who hold these beliefs aren't polite. Their personalities so abhorrent, vitriolic and unsympathetic. They hold such archaic views, reminiscing about a past that would benefit them at the expense of others.
To use eugenics as an example. Those who speak about it always, without exception end up isolating a single group that they believe is inferior. These people often hold adjacent beliefs that make the lives of other humans significantly harder, to say the least.