Kenneth Waltz's argument is entirely specious.
Yes, MAD is probably the only reason there hasn't to this point been a world war III. But you need to zoom out and judge this on a slightly longer timescale than 65 odd years
I think it's pretty obvious that the probability of a nuclear armed state entering into a confilct with another in any given year is non zero. In fact, if you look at the cuban missiles crisis, or the able archer incident, it's pretty obvious that that probability can be fairly high.
It's also pretty obvious that any major power nuclear conflict would result in the deaths of most of the worlds population, quite concieveably all of it.
Therefore, the probability of an absolutely catostrophic nuclear incident will asymptotically approach 1 the longer we have nuclear armed states. In my view our annilihation is assured if we keep these weapons around long enough.
Being willing to contemplate the destruction of the entire human race, rather than contemplate the destruction of your particlar political power base/ideology is to my mind the purest expression of human insanity.