I personally feel that having nukes around is never a good thing, per se, but the MAD angle is a legitimate one. Currently, no country is stupid enough to try and nuke anyone else, since that country will just nuke them back and everyone loses. On the other hand, I feel that, because of this style of politics, millions of deaths becomes a kind of scoreboard; whereas normal bombs have death tolls in the thousands, nukes kill hundreds of millions of people, instantaneously.
Let's say country A fires nukes at country B; country B has five hours to respond before the missiles touch down. It'd be impossible to evacuate the country, and even announcing to the population that they'll all die in five hours will lead to mass panic and rioting. So country B decides to fire back and hope country A loses more people than country B. Both sides lose; it's the objective of each side to make the other lose more.
The issue with this is that, when nukes come into play, populations of innocent civilians become like poker chips - no real value, just an abstract way of keeping score.