it's pretty easy to know that it doesn't matter (for the brain's purposes) whether or not my politics is objectively correct or not

Bolded the part I consider controversial. If you haven't characterized what sort of inference problem the brain is actually solving, then you don't know the purposes behind its functionality. You only know what things feel like from the inside, and that's unreliable.

Hell, if normative theories of rationality were more computational and less focused on sounding intellectual, I'd believe in those a lot more thoroughly, too.