Yes I'm familiar with non leftist thought - I only really started to identify with leftism about a year ago, having been something of an amorphous socially progressive conservative beforehand (having liberal social views but also believing in personal responsibility as the primary way to fix any and all social problems). I didn't even come into leftism through a normal way - I started learning about cybernetics and systems theory, then encountered Deleuze and through him fell into critical theory and then rediscovered Marx's critique of political economy, which tbf I did already have some reasonable knowledge of.

Intersectionality is not saying that those categories are all a person is - it's saying that those factors are predictive of certain oppressive tendencies society may have towards the individual. A common misconception I hear about leftism is that it is against treating people as individuals; this is not true, but at the same time denying that black people are oppressed in the US because they have individual identity is a non sequitur at best. The leftist ideal is actually that all people are free to pursue their passions and creativity, which is not something an innately collectivist ideology (like fascism for example) would promote.

I do think that a classless society is extreme compared to our current system, I wasn't denying that - but that doesn't mean that leftists area engaging in "extreme overgeneralising"; I still have no idea what that was supposed to mean. Honestly I see a lot of people critiquing left wing ideas using these really vague descriptors and I don't get why. If somebody has an issue to raise they should raise it explicitly so we can discuss it! Political discussion helps us all to learn.