Like there have never been insane rulers?
Plus nuclear deterrence only works against enemies with a defined infrastructure. Enemies like islamoterrorists have no defined infrastructure, hence no place to lob a nuke. You could make Afghanistan a radioactive glass parking lot and it would have no effect on islamoterrorists in Egypt.
Also, what good would nukes do if islamoterrorists decided to land on our shores and started blowing up malls and schools because they wanted to. Using nukes would be like setting yourself on fire to kill the leaches you have on your back.