In my culture (the American midwest) if two people are willing to voice conflicting views (good god if you're not willing to speak to up you will hear a whole lot though) they generally mutually agree to not talk about it at all. So my advice is usually to just not back down, and they will simply not talk about it to you.
Failing that, I would probably just stonewall the conversation. The moment they say some shit just tell them they are gross for thinking that way and refuse to continue talking to them. Let them know they are judged for being bad people, but otherwise don't bother actually trying to talk. Eventually, if they want to try to talk to you about politics, they will have to ask about yours. Then you have control of the conversation.