You apparently missed the fact that I think the claim that we actually could make ICBM attack impossible are so much baloney. (And here I thought I made the Microsoft comparison fairly clearly...)

Cost benefit analysis is beside the point. Spending money in pursuit of guaranteed failures is a waste of money. Doesn't matter how nice the result would be. If it ain't going to happen, it ain't going to happen.

If you want to justify the research for secondary benefits, well ask for the secondary research. Because that is all we are going to get. (Now defence contractors, that might be a different story...)

Cheers,
Ben