I remain very close with my sister, the flaming leftist. It does, indeed, require me utterly avoid saying anything about politics and current events on which we don't agree (which is most of them). I will point out that my sister, by contrast, feels no need to self-censor herself likewise to maintain the relationship, despite knowing perfectly well where I stand on issues. She is constantly popping off with her talking points and spitting out diatribes about whatever's on her mind, leaving me the choice of changing the subject or responding and thereby inviting her to start a fight.
Which just goes to show that leftists, no matter how nice they might be otherwise, are bullies at heart.