The same way one communicates with anyone of any ilk (nearly), you lay out your positions and why, and they lay out theirs. I had a good friend, an Irish fellow, very nice guy, he classified himself as a Maoist, though he thought Mao was too far right. He gave me a Mao pin. Fun guy, very smart, different background obviously, disliked every US politician, so we had that in common.
Another fellow I knew on line called himself a "libertarian socialist", I was fascinated. So, I asked him a lot of questions. My intent was to try and understand his views, not change his mind.
Now, there are plenty of extremists with largely emotional views devoid of any facts they dislike, and they are just for amusement, not serious discussion. But I believe I can have a discussion with anyone who has well founded beliefs on a topic.