By way of introduction, there are typically two ways of refuting someone's argument. The first is to go outside the bounds of the actual claim, looking for external, contradicting empirical evidence. This generally suggests that you first know where to go to get this evidence, and sometimes that can be a bit of work but it is, of course, a fairly common strategy.
The second way is to demonstrate that the claim itself is simply absurd because it is internally contradictory and unsupportable based on its own words. If you can pull that off, it's generally a lot easier since it's a lot less work. And herein lies the brain teaser I'm going to leave you with.
Based on a private e-mail from a friend (who apparently likes to prolong all of this suffering), I refer you to Mr. Gatsby's ... uh, Mr. Gillespie's opening salvo defending the privatization of Social Security. In hideously misrepresenting the actual logistics of the Bush plan, Mr. Gillatsby writes (in part):
The money for your Social Security account would come right out of your paycheck automatically. That money is invested in a conservative mix of stocks and bonds ... Those bonds will allow your account to grow at a greater rate than in normal Social Security funds.
Sure sounds like a good deal, don't it? And who will be the first to spot the gaping logical flaw in Mr. Gillatsby's description of how this scheme works? You don't even need to know the context of the passage above -- everything you need is right there.
The floor is yours.