TheStreet.com's Jim Cramer says people think the banks can't sustain the rally. Here's why they're wrong.

Sometimes, someone has to give the bullish, "On the other hand ...". There's a wide perception that the banks' good fortune of making money on the net interest margins -- the principal source of earnings besides fees this quarter -- can't last. Our old colleague Peter Eavis spells things out pretty succinctly and, shocker, bearishly in The Wall Street Journal this very morning in an article that should have you salivating for when the short-selling restrictions come off the financials and we can free-fire zone 'em again.

But how about the, "To be sure ..."? How about the, "On the other hand ..."? Or how about, "Some observers do point out ..."?

Nah, that would water down the article or even kill it outright.

Indulge me, for a second, on what I thought would have been a more provocative story for this stage in the rally, which is: Given all the bad news about earnings and losses and bad loans and auction preferreds, how the heck did the banks rally? Was it all a big joke, or is something else going on?

Then, from there, you say, "OK, what am I missing, because this net interest margin can't be banked on as people think it can be."