Well... The gain part would be that some worst evil would be destroyed. It is a shame of our civilisation what is happening there. Worse than a bomb, really.

Of course, the opposite part of precedent responsibility should be seriously weighted. It is more reasonable to wait until real rogue nuclear threats can be discerned.

I am pessimistic because I think that people are able to do very stupid things. Pakistan and India got a bomb, Iran would get a bomb, then Saudis and whatever next. Someone will see a "permanent" solution to some ethnic problem (Israel, for example), and go ahead... What do we have to leverage against that?