I was once on a tour in Provence that included the house where Nostradamus used to live, which features several windows that have been bricked over. “That’s because the government used to tax you based on how many windows your house had,” I volunteered to the group, trying to be informative. “And that’s why wealth taxes don’t work,” I added, trying not to be annoying.

I am not sure the tour guide — a proud Marxist, this was France after all, I expected nothing less — appreciated my editorializing. But it’s a relevant issue again as France considers a wealth tax, which would be as nonsensical today as it was 500 years ago.

Over the next decade, almost every rich country will have to face fiscal reality. All have expanded their welfare state to serve not only the needy but also the middle class, with expensive pensions, health care and worker benefits. But with an aging population, slower growth and rising interest rates, the math just doesn’t add up. Something has to give. In the meantime, U.S. and European politicians are grasping at one strategy they hope will allow them to avoid hard choices: soaking the rich.