Just replace “we” with “they” in any general critical remark, and you realize both what the person speaking really thinks, and how harsh it would sound if he/she actually said it. Using the first-person plural is both a way of being polite, and a way of being wimpy (while sounding noble).

The first-person plural allows people to criticize without seeming like they’re pointing fingers, or holier than thou.

And the guilt (as you point out)! The nobility of the suffering! The one thing that makes the We-sayer better than the They about whom he/she is using “We” is that he/she at least feels guilty about how terrible he/she is.

So even when a person says “We are [bad, selfish, lazy, etc.]” and means it of him- or herself, it turns into a penance which absolves the speaker. It ends up being a way of separating the speaker from the rest of the We; it turns the rest of the We into a They; the They remain guilty and unrepentant, while the speaker gets to feel a little better about him- or herself.

(C.S. Lewis said something about this phenomenon in one of his books, but I don’t remember which.)

Convenient indeed.