Everything that violates human right for example. Or direct threats to democracy.
I haven't come across one yet.
And indeed, there is no solution here other than to be tolerant of other opinions, which may come from very different contexts than your own.
american foreign policy often becomes european union migration policy. just remember that, for example, when discussing international affairs.
Having said that, I have to say that HN is one of the communities that is better at dealing with different opinions, from different places. It's much harder on Reddit. On Metafilter, it is absolutely impossible: anything far from mainstream American liberalism is considered taboo.
The only thing I'd add to your point is that while HN is certainly global (or let's say highly international), the community is still overwhelmingly from Western countries. (Not all hold pro-Western views, of course, but that's different.) This means that users from non-Western countries who want to contribute views that go against what is commonly believed in the West, have a hard time. We do what we can to help, but unfortunately it's not much, because the forces of large numbers and group psychology are unstoppable, especially together.
As a northern european, I for instance would say that I often find HN trend conservative, compared to the discourses in my country. But someone from a different part of the world could claim HN to lean progressive, based on their political environment.
So I don't think there is an easy way here. If one were to decide that HN should balance both-sides, who draws where the middle lies?