What are we going to do about North Korea if they DO get a nuc. wepons?

I do not see a problem with N Korea having a nuclear weapon,they probably have already, it is not just a technologie thats new , Why can the USA , France , India etc have those Bombs for what , if anyone uses them there wont be much left of this planet and us to worry about and I believe the Governments know that too and would not use them ,irrespective which Government , What harm has Iran or N Korea done ?Would America like it if other Governments tell them to stop their Nuclear production? My biggest worry is that America would be the first to use those weapons at some time.