I think it's really very good when people reconsider the things they've said in conversation. My goodness, you can still find things I wrote on the Internet ten or fifteen years ago, and I certainly don't think all of the same things now. I think that the evolution of personal viewpoints is normal, and healthy, and should be welcome.
However, I think it's really bad when you pretend not to have said the things that you previously did. To enforce this kind of ex post facto internal consistency is dishonest. Maybe not to-the-core dishonest, but certainly untrustworthy, and in general not the kind of conversational partner I want to have.
I think that de-publishing is much closer to (but not the same as) pretending you never said something than it is to reconsidering previous viewpoints. It does strike me as uncomfortably Orwellian, even if it is a private group doing it, rather than the government. I mean, how would people feel if the New York Times decided to remove every mention of Monica Lewinsky from their archive due to poor behavior on her part? If Warren Ellis is right, and Cory and Xeni are the "cut and paste editors of the Internet," then it matters, regardless of whether that job was thrust upon them or one that they willingly embraced.
Finally, wading through blog comments on this whole issue reminds me why it's a good thing to keep your conversations small in the first place.