Europe is as full of bad ideas as it is of bad debts.

Conventional wisdom says that sovereign defaults mean the end of the euro: If Greece defaults it has to leave the single currency; German taxpayers have to bail out southern governments to save the union.

This is nonsense. U.S. states and local governments have defaulted on dollar debts, just as companies default. A currency is simply a unit of value, as meters are units of length. If the Greeks had skimped on the olive oil in a liter bottle, that wouldn’t threaten the metric system.

Bailouts are the real threat to the euro. The European Central Bank has been buying Greek, Italian, Portuguese and Spanish debt. It has been lending money to banks that, in turn, buy the debt. There is strong pressure for the ECB to buy or guarantee more. When the debt finally defaults, either the rest of Europe will have to raise trillions of euros in fresh taxes to replenish the central bank, or the euro will inflate away.

Leaving the euro would also be a disaster for Greece, Italy and the others. Reverting to national currencies in a debt crisis means expropriating savings, commerce-destroying capital controls, spiraling inflation and growth-killing isolation. And getting out won’t help these countries avoid default, because their debt promises euros, not drachmas or lira.

Defenders think that devaluing would fool workers into a bout of “competitiveness,” as if people wouldn’t realize they were being paid in Monopoly money. If devaluing the currency made countries competitive, Zimbabwe would be the richest country on Earth….

Indebted governments have been pressuring banks to buy more debt, not less. As banks have been increasing capital, they have loaded up even more on “risk-free” sovereign debt, which they can use as collateral for ECB loans. The big ECB “liquidity operation” that took place yesterday will give banks hundreds of billions of euros to increase their sovereign bets. Bank depositors and creditors have figured this out, and are running for the exits.

By stuffing the banks with sovereign debt, European politicians and regulators are making the inevitable default much more financially dangerous. So much for the faith that regulation will keep banks safe.