North Korea and the bomb

So at what point does someone figure out that:

a) North Korea's government, living in a bubble and not a particularly stable one at that, is likely to use its nuclear weapons in a first strike situation; and

b) Not only would their strike potentially kill hundreds of thousands if not millions, but any retaliation is likely to do the same; and

c) It would be far safer for some other country - read, U.S. - to first strike their missile silos and weapons storage areas, limiting potential collateral damage to military targets.

I realize it's hard to take the North Koreans seriously, what with their goofy videos and all (see below), but at some point the calculus becomes unarguable - if a psychotic paranoid controls a lethal weapon, the safest course of action is to take it away before it can be used.