I'm not personally acquainted with every single Republican who went over to the Dark Side, but the ones I am acquainted with who felt strongly enough to take out an anti-Bush ad last fall are quite socially conservative. They're folks who have previously followed a perfectly straight party line for many years--you know, low taxes, strong defense, individual responsibility and independence, limiting government, cutting spending on social causes, ending abortion, etc.
I don't understand it and don't support it at all.
Yes, it is odd and hard to understand, but we also see that from time to time in some of the angry posts here. Thanks for sharing.