“The largest U.S. banks are accused of causing problems in markets ranging from energy to aluminum. Regardless of whether they’re guilty of market-rigging, as critics say, the charges raise another question: Why are the banks active in these businesses in the first place?

“Part of the answer is a point we’ve stressed before: They’re among the country’s most subsidized enterprises. The Federal Deposit Insurance Corp. and the Federal Reserve, both backed by taxpayers, provide an explicit subsidy by ensuring that banks can borrow money in times of market turmoil. Banks that are big and connected enough to bring down the economy enjoy an added implicit subsidy: Creditors will lend to them at low rates on the assumption that the government won’t let them fail.

“The subsidies arose because banks perform a special public service. The lending they do and the payments they process are crucial to the functioning of the economy. Problem is, access to cheap, subsidized financing gives banks a big advantage if they move into markets beyond their core business. That’s great for the banks, but it distorts the competitive landscape.

“Consider the recent mini-scandal in the aluminum market. Taxpayer subsidies gave the banks an edge in holding the metal. Subsidized financing — made particularly cheap by the Fed’s efforts to stimulate the economy with near-zero interest rates — encouraged banks and their clients to build bigger stockpiles than they otherwise would have, tying up supplies. If the bets were to go wrong and lead to distress at a big bank, the Fed would have to provide emergency financing for an activity that taxpayers never intended to support.”

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