I think that video demonstrates very well that all it takes is simple questions to reveal the weakness of these people. It just takes someone willing to walk up to them and say "what do you mean by that?" He didn't get sucked into defending Beck, he asked then for their proof to back up their signs--they had none.
"Why do you believe that and how did you come to that conclusion?" A Question no liberal will ever answer, because the answer is "I didn't think about it at all. Harold,a clever sheep, told me it was true. Harold is part of the herd, and therefore would not lie to me. Now excuse me, I have to go perch in this tree.