Yes, an attack on Iran's nuclear sites is a bad idea. So is the idea of an Iran with nuclear weapons. Hence, a dilemma.
James Fallows has a characteristically thoughtful post up about the latest Iran brouhaha, and comes to the conclusion (actually, he came to the conclusion quite some time ago) that bombing Iranian nuclear sites -- either by America, Israel, or some combination of states to be named later -- is a bad idea. We don't really disagree on this basic point. I think it would be reckless for either Israel or America to try to preempt by force the Iranian nuclear program now (as I wrote in this column, it would be smart to continue, and intensify, the sabotage programs that have already apparently slowed-down the Iranians, and tightening sanctions on Iranian banks, in particular, might have some impact). I tend to think now that an Israeli strike would be very ineffective and dangerous no matter what point in the future it is launched, in part because Israel's capabilities are so much more limited than America's.
As for the U.S., I believe two things: One, that President Obama is serious and sincere when he says that all options remain on the table and that a nuclear Iran is "unacceptable" to him, and two, it is a good thing that Obama is sincere, because I don't have much faith in the idea that the U.S. could safely contain a nuclear Iran, as some people have argued. President Obama rightfully fears a nuclear arms race in the Middle East, which is what would happen once Iran goes nuclear, and a nuclear arms race in the world's most volatile region could lead to a nuclear exchange, even an inadvertent nuclear exchange.