Economist Channel

Arnold Kling's Askblog quotes Robert J. Mann

Wal-Mart’s application to form a bank ignited controversy among disparate groups, ranging from union backers to realtor’s groups to charitable organizations. The dominant voice, though, was that of independent bankers complaining that the big-box retailer would drive them out of business. Wal-Mart denied any interest in competing with local banks by opening branches, claiming that it was interested only in payments processing. Distrusting Wal-Mart, the independent bankers urged the FDIC to deny Wal-Mart’s request and lobbied state and federal lawmakers to block Wal-Mart’s plans through legislation. Ultimately, WalMart withdrew its application, concluding that it stood little chance of overcoming the opposition.

Mann also writes

... I argue that permitting Wal-Mart to have a bank would have a salutary effect on the relatively uncompetitive market for payment networks. The dominant position of Visa and MasterCard, in which payments are priced above cost to subsidize credit, inevitably will give way to a world in which payment services are priced at cost, or even below cost as a loss-leader to attract customers to other goods and services.  

As the first quote shows, Walmart was only trying to process payments more efficiently -- because it already saw the chance to offer banking services, lend, and other banking functions would be blocked.

Arnold also points to this by Lawrence J. White.

Arnold sums up,

We are always told that we need regulation to protect consumers and make the financial system safer. That is the theory. The practice is that regulation very often gets used to limit competition. 

Many people in the US still do not have regular bank accounts, and perhaps wisely so as banks notoriously suck money from poor people with pesky fees. Yet cashing a social security check remains a problem. Imagine small town America in which Walmart also offers banking services.

If it's not obvious, Walmart banks would be much safer than traditional banks. A bank tied to a huge retailer would not be financed by astronomical leverage, and if the bank lost money the equity holders of Walmart would pick up the losses.

Walmart has also faced a lot of resistance and restrictions in opening clinics. Imagine small town America in which simple, cheap Walmart clinics can offer a much wider range of services.

It's worth remembering how much opposition Walmart already overcame. It was the Uber of its day. A&P, its predecessor, was widely opposed, as was Walmart. Walmart still faces union opposition -- as I left it was still blocked from operating in the city of Chicago. Imagine the south side of Chicago populated with Walmarts, Walclinics and Walbanks! Thank its legislators and regulators for protecting its citizens from that nightmare.

Update:

An excellent blog post by Larry White on Walmart's troubles in starting a bank. A primary obstacle is the rule that bank holding companies can't be engaged in "commerce." Larry also points out just how much the other banks use this to keep out competition.

the Dodd-Frank Act of 2010 placed a three-year moratorium on the granting of deposit insurance to any new (or newly acquired) ILC. Although the moratorium expired in 2013, bank regulators appear to have “gotten the message” that the commerce-finance barrier should remain intact.