A perfect example of this was the President's recent assertion that roadside bomb IEDs in Iraq were coming from Iran. The funny thing was, when reporters asked Gen. Pace, chairman of the Joint Chiefs, about this, he admitted that they have no proof of this. But it sounds good, and in fact, Bush's assertion received a lot more press, even after Pace's denial, than the denial. Examples like this are legion in the last four years. Remember Condi Rice's "smoking gun will be a mushroom cloud"? Yeah. Same thing. Sounds good, gets people riled up, and the actual truth is pretty much irrelevant.
"I believe it is an established maxim in morals that he who makes an assertion without knowing whether it is true or false is guilty of falsehood, and the accidental truth of the assertion does not justify or excuse him."