In what circumstances is it illegal to be a white supremacist or to preach a more radical version of Islam in the UK? It might be illegal to join certain groups but I don't remember people being convicted for having a belief or opinion.
It is only a preposterous example to somebody who sees everything in black and white, right or wrong. It is a spectrum and we are just talking about where you draw the line, which is going to be personal preference.
Take Zouma for instance. Some people couldn't give a **** that he booted his cat across the floor, they can hold that view but I don't care what their reason is for thinking that, I won't be their friend. They can be friends with each other and laugh about abusing animals together.
I have a pal who tries his best to defend some of the terrible shit Boris has done, we just don't talk politics. My personal line is somewhere beyond that so he and I can still get on but something doesn't need to be illegal for me to disagree with it enough that I don't want to involve myself with people who agree with it.