nuclear weapons can be a good method of deterring war. the idea of M.A.D. can be very good to keep the peace. its similiar to the idea that purse snatchers try not to go after the 200 lb women carrying shotguns but small frail women. nations, like people, try to prey on those who can provide them the most gain and inflict the least damage on them. nukes provide a balance between powers (until an effective defense shield is developed at least, but that will be decades).
There was a special on the manhattan project on the history channel a while ago and one of the scientists basically said 'up until 1945, the number of people who died in wars continued to grow exponentially until 1945 when the numbers dropped steeply and leveled off'.
of course in the hands of a nut it can be trouble. supposedly Joseph Stalin didn't die of old age, he was murdered by his inner circle because he was planning a nuclear attack on the US. Right now nobody knows if North Korea will nuke the US.
And, of the 9 countries that have nuclear weapons (France, Russia, US, UK, China, Israel, Pakistan, India, North Korea), 2 are among the 7 worst dictatorships on earth, one is nation that has alot of sympathy for terrorists, Russia is just recovering from 60 years of inhuman dictatorship and one is a nation that is on the brink of war everyday. Plus Iraq was on the verge of going nuclear. so 1/2 the nuclear countries are either dictatorships or very unstable.