The political compass can be separated in economical and social issues. Economically, HN is right-wing, as you say. It's full of libertarians. But socially, it's strictly left-wing. Things that get you flagged? Men and women are not the same, we should not turn the world around to appease to non-heterosexuals, perhaps people of different races/ethnic backgrounds/religions are fundamentally different (for better or for worse), all humans aren't worth the same, countries should have the right to manage themselves in any way they want without having human rights shoved into them by the west... Stuff like that cannot be discussed here.
And as I said, I don't know if it's a conscious effort by the mods, or those topics only incite flames so they have to be shut down. What I do know is that just yesterday we got https://news.ycombinator.com/item?id=21365411 on the front page (which is, quite literally, left-wing political propaganda) but something that criticised those points would be flagged in minutes.