Mankiw links to Krugman on why HMOs don't work particularly well. I think they're both right. Krugman is right to distrust HMOs, and Mankiw is right to distrust giving government that much direct power over his (and my) health. However, the whole weight of history supports the idea that we can't trust government, while only a few decades support the idea that HMOs are bad. Like a rational Russian in 1918, I'd be against the Czar and actively oppose the Lenin, and today I'm against HMOs and am actively against having even more government control over healthcare.