The best I've found is reddit.com/r/neutralpolitics. It's strictly moderated, with minimum comment lengths and required source links when making factual claims.

I too have not found a good place to have any type of political discussion. Even on HN it's better but still almost impossible especially if you have any type of opinion or have done anything in the past that doesn't align with what the majority of opinions are on this site.

Politics seem to work like religion in the brain. I'm not sure it's possible to have a good discussion.