A related problem is how to prevent over cavepeople from stocking their own caves with these weapons. What do we do about the North Korean cave or the Iranian cave?
Most countries are most powerfully concerned with protecting themselves. Both North Korea and Iran are mostly stocking weaponry and military knowledge because they are facing constant threats from the world's most powerful military that their leadership will be annihilated.
Iran is constantly being threatened with the use of force by one of the most powerful and belligerent countries in the region (Israel). It has a history of having its leaders deposed by the USA. It has a history of making deals with the USA, keeping its end of the bargain, and discovering the USA had no intention of doing so (while accusing Iran of being the problem). It is one of the only places where their particular religion is accepted in the region, with extreme intolerance of it from one of the other powerful nations in the region (Saudi Arabia). And it is one of the few countries who still care about the fate of the Palestinians.
There's a cost to answering this question wrong too -- the US spent the better part of last century toppling governments and installing sock-puppets, and it led to resentment, terrorism, and revolutions that brought even worse governments.
