Heavy is the head that wears Wal-Mart's (NYSE:WMT) crown.

For years, this megaretailer has been blamed for everything from mooching off the U.S. taxpayer to laying waste the town hardware store. It's been accused of beggaring the union worker and poisoning American babies. While all these charges can be debated, there's one thing I'm certain of: Wal-Mart's latest idea is bad for America.

I'm speaking, of course, of the switch to payroll cards.

Um, OK ...
An innocuous idea, you say? At first glance, maybe. Wal-Mart plans to exit the paper paycheck game over the course of the next few weeks, switching all employees to direct deposit if they have bank accounts, and if they do not, to "payroll cards."

If you've never heard of these gizmos, you'll find a quick primer on the subject here. But basically, a payroll card is a debit card onto which the employer loads the employee's salary. The employee can shop with a payroll card as with any other debit card, make ATM withdrawals, or even draw on the balance with checks.

So far, so good, and it's not even novel. Visa (NYSE:V) and MasterCard (NYSE:MA) both offer "reloadable" prepaid cards to their customers. Wal-Mart itself has sold precharged cards since at least 2007. Capital One (NYSE:COF), Citigroup (NYSE:C), and JP Morgan (NYSE:JPM) were quick to climb aboard. As for payroll per se, Sears Holdings (NASDAQ:SHLD) was one of the first entrants into the market when it began a payroll debit card program for employees in 2002.

Consume, consume, consume
And yet, just because an idea is popular doesn't mean it's good (cf health-care reform), and payroll cards are a case study in popular-but-bad ideas.

Payroll cards encourage spending and discourage saving. While paychecks deposited to a bank account begin earning interest for their owner from Day 1, funds loaded onto a payroll card do not. To the contrary, cardholders often pay a monthly fee for holding the cards. And many charge for ATM withdrawals, too.

So, far from being rewarded for saving money, payroll cards encourage workers to spend their cash as fast as possible -- before the monthly fees eat it all up. I suppose a company whose business depends on getting people to spend rather than save sees nothing wrong with that concept, but I don't like the idea. I think it's a retirement killer.

Foolish takeaway
As the nation's largest private employer, Wal-Mart widens a trail that many others are sure to follow. And if they do, Wal-Mart's latest idea will lead us all down a path to penury.

Disagree? Feel free. If you believe Wal-Mart's payroll cards are a good idea, post your thoughts below.

Fool contributor Rich Smith does not own shares of any company named above. Sears Holdings and Wal-Mart are Motley Fool Inside Value recommendations. The Motley Fool has a disclosure policy.