Have any plans for this Saturday? The nearly 100,000 people who have pledged to take part in Bank Transfer Day certainly do: closing their bank accounts. The idea is to punish “Too Big to Fail” banks by instigating a mass exodus to smaller credit unions and community banks. Though not technically affiliated with Occupy Wall Street, it’s a practical expression of the anti-bank anger the movement has wrought.

But if the executives at the country’s biggest banks have circled Bank Transfer Day on their calendars, it's probably not out of anxiety. Whatever the intentions of its organizers, Bank Transfer Day may end helping the very one percenters they mean to punish.

At the root of the problem is that many Bank Transfer Day enthusiasts have overestimated their value to the banks they patronize: Ultimately, not all bank customers are made equal. Most customers of banks aren’t wealthy (we know from the Federal Deposit Insurance Corporation that 57 percent of all deposits at big banks are under $250,000), but it’s the wealthy upon whom the business models of big banks mostly depend. According to Jennifer Tescher, President and CEO of the consultancy Center for Financial Services Information, banks typically earn at about 80 percent of their deposit revenue from the top 20 percent of their customers.

In fact, many small-fry checking account customers may end up costing, rather than making, banks money. Hank Israel, a finance consultant at Novantas, told me the average checking account costs banks somewhere around $200 a year to maintain, just to pay for staff and infrastructure. In recent decades, banks have covered these costs—and earned money—from run-of-the-mill checking account customers in two ways. First, by milking forgetful account holders for overdraft fees; second, by hitting merchants with “swipe fees” every time those customers used a debit card (to the tune of 44 cents per swipe). But last year’s Dodd-Frank financial reform legislation put a damper on both those revenue streams: On the one hand, by offering protections against overdraft fees; on the other, by cutting in half the debit card fees that could be collected from merchants (the latter by means of the so-called “Durbin rule”, named after the Senator from Illinois who insisted on its inclusion in the legislation). Overall, Israel estimates, banks industry-wide are out somewhere between $18 and $25 billion as a result of the Dodd-Frank changes.

The law undoubtedly offered considerable peace of mind to holders of normal checking accounts. But it also had an unintended consequence: In the eyes of banks, Dodd-Frank transformed low-balance debit card holders from potentially profitable customers into almost-guaranteed liabilities. Israel estimates that a customer now has to maintain an average checking account balance of about $25,000 before a bank can profit from it. Making matters worse is that the big banks are experiencing a sort of hangover from the boom era before 2008. In those years, the banks were giving out loans so feverishly that they were gladly adding checking account customers simply for whatever additional capital they could provide. Now all those checking accounts they added in a binge can pose a burden. Without the ability to levy harsh overdraft fees or charge as much for “swipe fees”, there simply isn’t much incentive for banks to keep debit card users aboard at all anymore.