Nate Silver points out that in the last decade, there have been six attempted terrorist attacks on U.S. commercial flights. There have been in that time, 99,320,309 flights. Ergo, your odds of being on a plane that is the target of a terrorist attack are currently running around one in 16,553,385. We all do things a lot riskier than that every day without hesitation.
By the way: If you aren't checking out Mr. Silver's FiveThirtyEight.com, you're missing a lot of calm, statistics-based discussions about health care and insurance and what it's all going to cost us. If you read his site and those to which he links when rebutting, you'll get a pretty sane overview of the situation.