Talking heads are screaming about "naked" short sellers driving down the banks, but don't believe it. Naked shorts may shave off some points, but the blame still lies with the same few culprits:
1) The banks themselves. Investment banks, by nature, are supposed to be the best risk managers in the world if they're at all interested in long-term survival. They weren't, and a few years of unsustainable profits from building, trading, and selling risky mortgage debt are currently destroying what just two years ago were the safest bets on Wall Street.
2) Regulators. The Federal Reserve, the SEC and the Treasury Department are now in a frenzy to fix a problem that could have been halted over the last decade. The rise of securitization went broadly unchecked. Now, after the damage has been done, they're finally getting some teeth.
3) Ratings agencies. Standard & Poor's, Moody's, and Fitch get paid to rate debt. That conflict of interest alone should have made their opinions suspect.
In the meantime, the SEC's moves to stop naked shorting are really just a finger in the dike. The SEC has been asleep at the switch. Chairman Chris Cox has oddly been MIA during most of the crisis, leaving Hank Paulson and Ben Bernanke to lead the charge. Remember, when this is all over, he's the one that said no to extra regulatory power (and even extra funding) for the SEC before the crisis unfolded.