Technique: Demand sources and reasoning of your opponent's argument if you are unable to refute the argument outright. Ask, "and that is based on what?" or "How do you figure?" The answers to these questions will be easier to crush than the original assertions. Also, If they can't produce a source or they sight some suspect source (e.g. NY Post or the Washington Times or some other partisan source) then laugh away their credibility and say that such a source is a bunch of garbage. Question their sources. This distracts them from their point, interrupts their flow, insults them and often they won't recall the source of their information or even better, the source will be an easy target of ridicule and/or Character assassination, not to mention a convenient distraction from the issue at hand.