Very true. I don't know if I should have noticed it if it hadn't been pointed out to me (I gave up making a conscious attempt to believe the morally 'correct' line on various different social issues back in my twenties, when I discovered it was easier to accept that I was a vile unreconstructed bigot than to keep struggling to meet the latest demands) -- but I am very aware of my own knee-jerk rejection of any set of opinions that don't reinforce my own, and uncritical espousal of anything that tends to back them up. And this despite a conscious attempt to engage my intellect and disengage my emotions, and to understand that it is salutary to be exposed from time to time to the viewpoint of someone who doesn't share your bias, and that the possibility should at least be considered that they might be unappealingly right in some things and your cherished fluffy certainties might be wrong.

So the amount of mental effort that is required just to to entertain the awareness, let alone to do anything about it (you can't change human nature, as the Reluctant Cannibal put it), is tremendous.