MEGAN MCARDLE: Tragedy of the Public Good: Why the U.S. Shouldn’t Quit NATO.

The latest news is that Defense Secretary James Mattis has told NATO allies that if they don’t start carrying their weight, the U.S. is going to “moderate its commitment” to the region. Now, as an abstract matter of principle, I’m firmly behind this. Only five NATO countries actually hit their targets, and three of them are a lot poorer than the sponging grifters that have cut their militaries back … while enjoying the safety of the U.S. security umbrella.

The freeloading countries don’t even send a fruit basket to Washington to say thanks. In fact, as a rightish American who’s spent a bit of time abroad, I can personally attest that many of those NATO members’ citizens feel free to disparage our massive military budget, as if their smaller budgets were some sort of moral sacrifice rather than an unearned benefit paid for by U.S. taxpayers.

There, I got that off my chest. I hope we all feel better.

Nonetheless, even for me, Mattis’s statement is a sort of “gulp” moment. The Europeans aren’t the only people who benefit from the American security umbrella. The fact that the world’s biggest rich economy is willing to spend so much of its GDP on the military doesn’t just mean that other countries don’t have to; it also means that other countries don’t bother, because they can’t possibly catch up.

Like dealing with slobbish roommates, it may make sense to keep cleaning the toilet yourself, but a credible threat to leave may encourage them to do a bit less free-riding.