The Non-Proliferation Treaty embodies the commitment of the vast majority of the world's states to prevent the spread of nuclear weapons into the possession of additional countries.
The "bargain" under which this commitment was achieved includes preserving and enhancing access to the benefits of civil nuclear energy for non-nuclear-weapon states in good standing under the Treaty and pursuing, over time, the elimination of nuclear weapons from the possession of those countries that now possess them.
The goal of the NPT is important because every additional state that possesses nuclear weapons represents an additional set of possibilities for the use of nuclear weapons in conflict ( bringing immense destruction and risk of escalation ), as well as additional possibilities and temptations for the acquisition of nuclear weapons by still further states and by terrorists.
The existence and strength of the NPT itself are important because the goal of preventing proliferation cannot be attained by one or a few states acting alone, no matter how powerful those states may be: Attaining the goal requires the commitment and cooperation of the world community acting in concert to limit the spread, and monitor the use of, the technologies most directly relevant to acquiring nuclear weapons.
Every weakening of the NPT — whether through a state's refusal to join, withdrawal after having been a party, suspected cheating that is neither cleared up nor called out, or flouting by nuclear-weapon states of their side of the "bargain" — weakens the belief of the world community in attainability of nonproliferation goals and, accordingly, weakens the will of individual countries to participate energetically in the measures needed for success.
Any government concerned about the dangers from the use of nuclear weapons by either states or terrorists, as all governments ought to be, should be doing everything in its power to strengthen the NPT and nothing to weaken it.