Read the full piece in Bulletin of Atomic Scientists here.
Put simply, spreading nuclear technology spreads the ability (in whole or in part) to make nuclear weapons, and the institutions created to sever this connection have shown they are not up to the task. Unless this situation is reversed, the problem of turning the recently approved UN treaty on delegitimizing nuclear weapons into a treaty on disarmament acceptable to current weapon states may be impossible to achieve. A faulty nonproliferation regime is not the only impediment to nuclear disarmament (deterrence in the absence of nuclear weapons must also be achieved), but no weapon state will give up its weapons if it lacks confidence that other, possibly unfriendly countries will not arise to challenge them with a nuclear arsenal. To understand what must be done, it is important to know how we got to the current unacceptable situation.