A nuclear deterrent gives us the ability to defend ourselves and (as it says on the tin) deter those states who have/are developing weapons, from using them. You only have to look at the Dr. Khan network of recent years, demonstrating the modern proliferation of nuclear weapons to prove that the world does not yet have complete control over who develops nuclear weapons.
As for whom we are to deter, North Korea I would initially suggest, as they are producing missiles with greater and greater ranges. And there are a whole host of states queuing up to 'have a pop'. And are you saying you can predict who or what will appear in the next five, ten or even twenty years? Nuclear weapons are here now; we must come to terms with that. As Thatcher said, "You do not cancel your insurance policy, just because there has been a sudden decrease of burglaries in your neighborhood."
And as for the Cold War, what would you suggest was the reason for the relative stability was? Please don't suggest bi-polarity.
