You don't even have to go back to the 1930s. You just need to spend a bit of time around left activist types. Some are lovely, but for far too many, having an identity that revolves around self-righteousness, being morally superior because they care so much about the oppressed of the world, it gives them a permission slip to be giant flaming arseholes.
If you could bring Orwell to the present day in a time machine, he'd recognise people like Owen Jones or Richard Boyd Barrett as very familiar types.
And it's not a far left thing either. Plenty of bad shit happens in mainstream Labour politics. Not that bad things don't happen elsewhere, but the combination of self-righteousness and arseholery is something I associate with either left wing politics or certain religious subcultures.
I suppose I get triggered by people like TGF using "left" as a synonym for "nice", when that's far from my experience.