EDIT: I guess there are those who disapprove of Stuxnet because it probably violated some laws. I think it was awesome.
The problem with your plan, even from an amoral realpolitik perspective, is that the Iranian program cannot be prevented forever with 100% certainty. There's a possible future world where they end up with nuclear weapons after 30 years of assassinations, and that's the world where they'd be the most likely to make use of them. There are a lot of ways it could happen - maybe they build two plants and the west only gets one of them, maybe North Korea makes a donation to the cause. Maybe they set up a bunch of innocent scientists in the secret but not secret nuclear theory department and let their enemies waste time clandestinely assassinating their theory group while they manufacture the real weapon based on plans obtained elsewhere. When you're killing civilians, you're in a state of war, and although being in a state of war has had very indirect consequences for the US over the past 50 years, that's not guaranteed to go on forever.
Iran has about 80M innocent civilians living there. Even if you think of the leadership as holding them hostage (not too far from the truth for many countries...), that's a lot of hostages to sacrifice.
Do you realize that stating we must use "any means necessary" to prevent Iran from acquiring a nuclear bomb is expressing the desire to obliterate a sovereign nation? What means are acceptable for preventing your possible aggression?
>We can, in fact, ensure that they are incapable of making nuclear bombs. A country with stone-age technology is not going to be enriching nuclear fuel.
So you're fine killing however many millions of Iranians to prevent them from having the potential to kill a large number of people.
Shure there is, countries follow their national interest.
Beyond that - all it takes for Russia or China to provide Iran with nuclear weapons would be Israel or US pushing it too far.
Actually, that may already be something past the point - at this point an attack against Iran will be interpreted as an attack or prelude to attack against Russia or China.