If you go to any tea party event, you'll hear some crackpot stuff and see some people dressed up in crackpot costumes (tricorner hats etc.). By "crackpot," I mean stuff so outré that even movement conservatives know it's crazy and want nothing to do with it. Of course, it gets reported in the media occasionally, and when it does, snarky liberals have a field day with it.
But does this scare off anyone on the right? It does not. They ignore it, or dismiss it, or try to explain it away, and then continue praising the overall movement. The fact that liberals have found some hook to deliver a blast of well-timed mockery just doesn't faze them. They know whose side they're on.
So Krugman is right: liberals need to take the same attitude. Are there some crackpots at the Occupy Wall Street protests who will be gleefully quoted by Fox News? Sure. Are some of the organizers anarchists or socialists or whatnot? Sure. Is it sometimes hard to discern a real set of grievances from the protesters? Sure.
But so what. Ignore it. Dismiss it. Explain it away. Do whatever strikes your fancy. But don't let any of this scare you off.