There are, at the very least, two Andrew Sullivans. It is one thing to have changed your mind on the conflict in Iraq. It is quite another to do a complete 180 on the broader philosophical issues of the day without having even remotely laid the intellectual groundwork for having done so.
The former is a respectable and understandable shift in position. The latter only works if people completely forget all of the stuff Sullivan wrote in the past. And of course, thanks to the Internet, no one forgets.
Except, perhaps, for Sullivan.