Is there room for doubt as to the value of factual truth in all circumstances; is it always wrong to believe untrue things; is it possible to both believe and not believe something at once? In essence it's a position driven by the human brain's inherent cognitive flaws and limited reality-perceiving abilities - I sketch it very briefly. But if we're just not that good at truth & reality, can we doubt that these things are supreme values/virtues?

It's not morally wrong to believe untrue things. Our heads don't explode if we believe contradictory things, or believe without anticipating that the consequences of the belief being true will actually occur. There are probably situations where it is better to be happy than right. Nevertheless, on balance I want to know what the world is like because not to do so seems to leave me exposed to accident or malice (the latter's especially interesting, as there's clearly a niche for exploiting people who don't know what the world is like, which can be occupied by both people and ideas). I want others to know what the world is like because I don't exist in glorious libertarian isolation: their decisions will affect me, I feel empathy for them, and I'd rather neither of us got caught up by the bad stuff we could have seen coming if we'd only been looking. We're not good at truth and reality, but I don't see that as a reason to give up.