I thought this post of The Dude's on MAD's thread about angry exmormons was very insightful:
No, that's not it. They aren't embarrassed, they aren't trying to "convince" themselves that they did the right thing. Ex-Mormons just want to re-live the thrill of victory over a false and oppressive world view (in their opinion). Unlike others who doubt but stay in the church, the ex-mormons had the balls to say "the emperor has no clothes!" and let the chips fall where they may. It's stimulating to explore that break-out moment again and again, and it's fulfilling to help others do the same whenever possible. That's what motivates vocal ex-mormons.
It's the same as what motivates a new Mormon convert to share the gospel with his friends and family. Does it sound right to say the new Mormon is motivated to speak up by "self-loathing" or "embarrassment by the former non-LDS self" or "convincing themselves that they did the right thing" or "to prove to themselves that they were smart in joining?" Not really. It's nuts to psychoanalyze a vocal convert in this way. And the same goes for psychoanalyzing a vocal de-convert. They are motivated by the chance to re-live the "big moment" and help others do the same. It just feels good in an egotistical sort of way.