What do you think feeling shame means?
You are scared that you might be ostracized from the group
But I feel shame about things that other people don’t even care about.
You are scared that you should be ostracized from the group.
That seems unrelated to the social realities. Why would evolution bother to equip me with a feeling for that?
Because you need to be able to justify yourself verbally. It is important that you think you should not be ostracized, so you can argue for it. Even if nobody shares your standards, if other people try to ostracize you for some stupid reason and you—for other reasons—believe that you really should be ostracized, then you are in trouble. You want to believe wholeheartedly that you are worthy of alliance. So if you don’t, an alarm bell goes off until you manage to justify yourself or sufficiently distance yourself from the activity that you couldn’t justify.
(From a discussion with John Salvatier)
Speculation time: Would this predict that shame-prone people have bigger, deeper identities? Identities seem like a good place for storing those justifications, and those justifications look like a candidate for the reason we have identities in the first place.
Shame appears to be a reaction to perceived norm violation, so shame-prone people would be those with strong and restrictive internalized social norms.