In my experience from lurking around Lemmy, it seems that the big instances are largely populated by stereotypically "reddit-left" people, which includes finding a lot of things offensive (whether they're actually offended or not) and being relatively hostile to people who don't seem to share their worldview, seemingly considering it the default that everyone should know and accept. You can see it in this thread as well.

Not being an American and being culturally outside of american partisanship, this has been quite the disappointment for me, but what can you do.