Bank stocks fell for the second straight day Monday, as Bank of America (BAC) and Morgan Stanley (MS) sank within 5% of their 52-week lows. Another big trading bank, Goldman Sachs (GS), rose modestly but remains just 6% above its low of the past year.

The selloff is the latest sign of investor nerves over the banks’ true health. Both BofA and Morgan Stanley are trading substantially below Wells Fargo analyst Matthew Burnell’s estimates of their tangible book value, and Goldman Sachs is trading just above.

That’s unusual in itself, as banks over the past 20 years traded at an average multiple of 2.6 times tangible book – a rough proxy for the amount a bank might fetch in a fire sale, not that it would ever, ever come to that.

In any case, the implication is the market doesn’t trust the bankers any more than any of the rest of us. In part that’s because it seems reasonably clear the costs of the banks’ bubble-era misbehavior aren’t going to be neatly tallied any time soon.

That will, sniff sniff, hold down returns that already are nothing to write home about, except in anger and exasperation. And there lies the promise in this trend.

Fow now, Burnell blames the selloff trend on factors including “renewed headline risk related to potential legal actions against MBS providers” – such as the government lawsuits being pursued against Deutsche Bank and being considered against other big banks.

There is also, of course, the trading slowdown that stands to sap results at the big Wall Street players, and a slowing economy that may yet hold up the banks’ efforts to lend more money for what seems like the millionth time.

The bad news for those holding financial stocks is that the banks are looking like just as bad a bet as they did over the past decade, when they were the sole sector of the S&P 500 to turn in negative annual returns.

The good news is that if investors keep losing money on these dogs long enough, they may do what our political “leaders” have been too craven to do and demand that the bankers break up their idiotic, unsafe-at-any-speed empires. It seems like a stretch now, but a long run of zombie stock performance has a way of changing things.