The GSE's didn't start this crash. What really put the GSE's in the corner is when they bought bundled securities furnished by lenders. Those are what turned out to be toxic assets subject to clawbacks under the Obama Admin.
The GSE's were merely the first to be bailed out. The bailout & FRB action took care of incestuous lenders each using over valued paper as reserves in fractional reserve banking methods, leveraged at up to 30:1.
They had to keep selling more MBS paper to keep that going, so they kept getting more "innovative". When investors wised up, quit buying, they were left holding the (empty) bag.
The smartest among them changed course early, bet heavily against MBS in the synthetic derivatives market, buying protection from outfits like AIG. First, take a cut off the top in creating bogus securities, then bet against them, knowing the other guys were pulling the same shit you were.
Anybody who thinks there weren't any winners, really big winners, really has shit fer brains.