With friends like Frederic Mishkin, the Federal Reserve doesn’t need enemies.

The former Fed governor who co-wrote a book with Ben Bernanke on inflation-targeting has argued in the Financial Times that some financial bubbles aren’t so bad.

As long as they’re not fueled with leverage, the economy can stand a bubble or two, so there’s no need for central bankers to get trigger-happy and start raising rates from the zero-bound levels where they’ve been for nearly a year. Or so he argued.

This is a line that current policymakers should be adamant about not crossing. Keeping rates low is one thing, telling investors some bubbles aren’t so bad is quite another. It not only ignores policy missteps in the last downturn, but it threatens to take speculative risk-taking up another notch.

It’s especially the wrong message to send financial markets that are already giddy.

The dot-com aftermath rattled policymakers enough, however, for the Fed to drop interest rates to 1 percent while willfully ignoring signs that such policy contributed to an unprecedented credit binge. This is why regulators need to be especially tough with their charges if they want to keep wielding extraordinarily easy policy.

Keeping big bank leverage ratios low could go far to cap future excesses. Moving quickly to establish a private sector, rather than a taxpayer, safety net — there’s been talk about contingent capital — would be another way to counter the industry’s tendency to be led astray by the promise of easy money.

Just don’t try to play down the trouble with bubbles.