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."

And then the "a-ha!" moment, but one that is so bullish it can't be written because it so not in keeping with the Journal, or at least not until Rupert consolidates his bullish upbeat control over things and scares the living daylights out of all of the resident "I write negative stuff, get someone else" scribes.

That "a-ha!" moment is, well, one reason people like the banks is because maybe the net interest margin is going to EXPAND! Maybe we are looking at this too negatively. Maybe the Fed sees the dollar turning here, gold crashing here, oil plummeting here, and recognizes that there is now no real inflation to speak of or just maybe actually considers homes as part of the index (that homes aren't in the inflation index is preposterous but true) and realizes there is deflation and it cuts rates again.

Not only that, it would make sense, because in a world where there is no real demand to buy homes, why shouldn't the 30-year yields come down dramatically, making it even more obvious that the fed funds rates are too high.

And we could save the banks a heap of money as we jack up the FDIC payments for all of the crummy depository institutions about to go under, simply by taking the rate down enough to where the banks can play the curve, or invest your deposits almost risk-free at another short-term place in the curve, a la 1990.

It is tough to think about the Fed cutting rates when so many people believed just a month ago -- totally wrongly, but they never admit that -- that the next move is to tighten. They can always blame the collective wisdom of the futures as causing their lack of judgment -- oh, the luxury of being able to excuse being wrong, I treasure it! But wrong they were.

To me, though, getting back to what I see going on, not only do I expect the net interest margins to last and be terrifically profitable for some time to come, I also expect that they are going to expand.

So, what does it all mean? It means that as the short-sellers align themselves to take aim at the banks (as they are about to do), be careful; after taking the initial blows, the banks could be headed higher if oil goes to $110, as I expect it to, because the Fed has room to maneuver and even this "we don't move unless there is a crisis" Fed might actually want to be a step ahead for a change.

Even if they aren't, we can expect a crisis pretty quickly judging by a couple of bank stocks that are still going down even in last week's beautiful (pejorative!) rally.

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Jim Cramer is a director and co-founder of TheStreet.com. He contributes daily market commentary for TheStreet.com's sites and serves as an adviser to the company's CEO. At the time of publication, Cramer had no positions in the stocks mentioned.