Joe Carter at Evangelical Outpost has begun a series of posts on how not to argue. His first recommendation is to avoid hyperbole because it just makes you sound stupid. He says this about the use of gross exaggerations in an argument:
An example of a rule of thumb that I find to be particularly useful in helping to avoid problems is to avoid, whenever possible, willfully stupid people. Intelligence is, of course, a relative concept and everyone (except for the World's Smartest Person) is just a little less bright than someone else. Willful stupidity, however, is distinct from IQ because it consists of a moral failing: Choosing to be dumber than you have to be.
One way to recognize a willfully stupid person is to examine the role hyperbole plays in their rhetoric. Take, for example, those who, like Pulitzer-nominated author Stephen Pizzo, say that "George Bush is the worst president of the United States of America, ever. Hands down." Whenever I encounter such people I walk the other way for fear that such stupidity might be contagious. For anyone to make such a claim would require a basic understanding of Presidential history, an objective standard for comparing other Presidents to George W, and an ability to make nuanced judgments. In other words, it requires the very skill set that would generally prevent a person from making such an inane claim in the first place.
(I should note that this is not just a failing of left-leaning progressives. Willful stupidity is certainly not a partisan issue; we heard the same sort of claims about Jimmy Carter and Bill Clinton. The only difference is that Bush became President during the Age of the Blogosphere when the effects of echo-chamber ranting became more pronounced.)
The problem with making such a hyperbolic claim is that such exaggerations are not meant to be taking seriously. When the person who makes them treats them as if it were a rational claim then it shows that they themselves are not worthy of being taken seriously.
[If you're] inclined to disagree with this particular rule of thumb....I recommend you consider how you apply it in your own life. Think of the people whose analysis and judgment you most trust, the ones you consider to be sober and scrupulous thinkers. Now think of the people who are most prone to exaggeration and to making comments that amplify certain aspects out of proportion to reality. I suspect that, like me, you won't find much overlap between the two groups.
Good advice. We always thought that people who use wild and crazy exaggerations in their arguments were the dumbest people ever. Hands down.