Ummmmm.....they were synthetic CDOs. When you sell one to a "client", of course you're betting against them. You're the other side of the trade.
It's like calling your bookie and placing a $10 bet on the Cubs and then whining after the Reds win and saying, I didn't know he'd be cheering for the Reds. Doofus, that's what bookies do, take the other side of the trade.
Except that in this case, when the bookie took the bet on the Cubs, he knew that the entire team had gastroenteritis and wouldn't even make it to the dugout, much less play the game.
???
Umm... No they don't.
Bookies couldn't care less who wins and loses. That's why they spend a fortune coming up with a "line" that attempts to even out the bets on both sides. That's also why "the line" moves when the betting gets too heavy on one side.
Bookies make their money on the "vig". It's their commission for handling the bets.