I love Maher's show and have seen him combat these loons a few times--usually members of the panel.
I saw some so-called truthers yesterday when I was out and about in Portland. They were waving signs about 9/11 being an inside job. The most mind-blowing part was that cars were constantly honking to show support. Their misunderstanding of what happened that day has turned into a true religious movement.
When you are shouting and waving a cardboard sign on a street corner--regardless of what you are advocating--it's time to reevaluate your belief system.