Can people not tell when someone just nakedly and actively hates them?

They can, but they refuse to admit it when the person nakedly and actively hating them was the person they voted for. Not defending Biden would be an admission of guilt, of being to blame for this, and they have to deny that at all costs. They need to believe that this isn't their fault, that they made the right choice and that they can comfortably make that choice again. If something threatens that assumption, the defense mechanisms fire up automatically, as pure reflex, without them even noticing that they're entering the cope zone.