Well, finally someone delivered the response that such questions should get, and that someone is Barney Frank.
For those of you who are audio-challenged and reading along at work:
Wackaloon: Why do you continue to support a Nazi policy, as Obama has expressly supported this policy? Why are you supporting it?
Frank: When you ask me that question, I am going to revert to my ethnic heritage and answer your question with a question. On what planet do you spend most of your time? ... Do you want me to answer the question? Yes. As you stand there with a picture of the president defaced to look like Hitler and compare the effort to increase health care to the Nazis, my answer to you is, as I said before, it is a tribute to the First Amendment that this kind of vile, contemptible nonsense is so freely propagated. Ma'am, trying to have a conversation with you would be like trying to argue with a dining room table. I have no interest in doing it.
(Also note the shout of "Hitler didn't start with the Jews" somewhere in the background.)
Let future town hall speakers take that as a lesson: This is the way to deal with those people. Don't waste your time trying to reason with someone who's beyond reason. These people aren't trying to engage you in debate; they don't want their questions answered. They want to stand up and shout, be disruptive, propagate a myth, show off for their fellow wackaloons, maybe get on TV. And when you try to seriously address their questions, you only lend validity to an inflammatory statement that has none--and allow them to monopolize time that could go to someone with a realistic concern.
This is something that has pissed me off about the media for years now. In the interest of "fair and balanced" reporting, they think they're obliged to always give equal time to both sides of the story. Is this a good practice most of the time? Sure. But when one side is presenting a reasoned, reasonable argument and the other is coming from a place of fantasy and nonsense, giving time to that other side is a waste of time and makes something seem valid that clearly is not. If one side is saying, "We're 37th in the world for health care, nearly 47 million Americans are uninsured, and we see universal health care as the best way to address that problem for reasons A and B and C" and the other is saying, for instance, that Obama wants to send government agents into your home to brainwash your children, no. That other side does not deserve equal time. Nor does "Obama wants to kill your grandmother." Or "Obama is another Hitler."
By all means, if someone comes to you with a rational argument, talk with them. Engage in conversation. Give them a platform to make their point. Maybe you'll convince them. Hey, maybe they'll convince you. But when someone comes to you with "Obama is Hitler" or "Obama keeps an enemies list of anyone who logs on to a government Web site, and by the way, he's from Kenya," do not give them a sense of respectability by engaging. The only way to respond to them is the way Barney Frank did--that their baseless, inflammatory comment isn't worth your time or energy.