nuclear weaponry: a deterrent to proliferation?

In a Wall Street Journal interview with former U. S. Secretary of Defense James Schlesinger, Melanie Kirkpatrick raises the topic of nuclear deterrence, a timely one given the current U. S. president’s trip to Russia.  Speaking of the massive U. S. nuclear arsenal, Schlesinger argues that it is a necessary assurance for U. S. allies; otherwise, he claims, nations such as Japan would quickly build their own stockpiles.  Thus, he asserts that such nuclear weaponry is, counter-intuitively, the best possible deterrent to nuclear proliferation.  It is not, in this account, the existence of such weapons, but instead the actors holding the weapons that matters in the end.  At the risk of quoting Stephen Colbert, one may point out that only the U. S. should be trusted with such weapons, since that nation is the only one that has ever tested them on civilians.  What, though, is a serious position for those opposed to the continued existence of such weapons to take?  It seems that incremental downsizing of the arsenal(s) is the best that can be hoped for.