Think contractually. It's harder to move Chris Webber than Kenny Thomas, Williamson, etc. Petrie is taking a risk, but it makes sense, Webber has missed about half a dozen games with knee-related soreness this year, is 31, and has a contract that lasts several more years. The Kings probably weren't going to win the championship this year, and it's better to rebuild while the rest of your core (Peja, Bibby, Miller, etc.) is still in their primes. It would have been a much better deal had it been for expiring contracts, though. I wouldn't bash Petrie until the end of the summer, if the roster doesn't look significantly improved. Just MO.
But you’re right about one thing; on its face, this trade looks downright awful and makes no sense. But if Petrie has proven anything, it’s that he’s a very prudent GM.
IMO, it was a move for the future, so Kings fans' best approach is to wait and see.