For 15+ years, I've run a sports forum and it is inevitable that societal/political debates emerge in many threads. In recent years, they've become increasingly as you describe. There's almost never a calm, reasonable comment. People get at each other's throats and slinging left-right insults immediately.

I think a lot about how @PG almost never posts on HN any more. Might be wrong, but I suspect he's come to resent some of the discourse/attitudes and time-wasting here.