> 1. How many people might notice, but think that the mistake was theirs, and even argue for the opposite of their position in order to save face?
Probably most of them. This mechanism has been described by Cialdini as "Commitment and Consistency". Marketers abuse this in a clever way by ramping up commitment. If you answer a bunch of seemingly innocent questions to make you look good ("I often go see opera"), you have made a small commitment. Then it can be leveraged to sell you an expensive opera discount card ("For a person who visits opera so often, it would be irrational to turn the offer down".)