> the extreme cost of SDI meant that there was enormous opportunity cost. And on another angle, marginal costs greatly favor the offense over the defense. The

> the extreme cost of SDI meant that there was enormous opportunity cost. And on another angle, marginal costs greatly favor the offense over the defense. The mutually-agreed ban on MIRVs has ameliorated this, but still, in SDI scenarios the offense has it much easier and cheaper than the defense.