All of this assumes that the folks on the other end (folks who actually HAVE ICBMs) are complete and total idiots and can't calculate trajectory through triangulation and intersection. That is to say, in a round-about sort of way, that the two countries in the world (Russia and China) from whom we might actually have to worry about a nuclear response are both perfectly capable of determining within seconds or minutes of launch (at the outside) whether or not we're actually launching a missile at them. Of the other nuclear powers, it is my contention that they are either incapable of detecting an ICBM launch - OR- incapable of responding in any appreciable way (MAD would stop them but only to the extent that THEIR destruction would be assured) - OR - such strong allies of the U.S. that we needn't worry about this scenario.