In my Legal Writing class yesterday, the instructor talked about logical fallacies that we should avoid in our persuasive writing. Among the common fallacies is the argument ad ignorantiam:
ad ignorantiam (appeal to ignorance): arguing that a claim is true just because it has not been shown to be false. A classic example is this statement by Senator Joseph McCarthy, when asked for evidence to back up his accusation that a certain person was a communist: "I do not have much information on this except the general statement of the agency that there is nothing in his files to disprove his Communist connections"
The instructor used another example, the U.S. claiming that Saddam Hussein has WMDs because he hasn't been proven not to have them. Most of the class laughed in appreciation and we went on to have a lively discussion of other common logical fallacies and whether the U.S. case against Iraq contains them as well. It was pretty clear that nearly all of us were very skeptical about the whole thing. We also discussed whether Colin Powell was using hearsay evidence that would be thrown out of any court of law.
It may be that paralegal students are not a representative sample of the population, but certainly my impression from this and other discussions at school is that there are a lot of intelligent, well-educated people that Bush is failing to convince.