David Cameron insists we must replace the Trident nuclear weapon system because the future is uncertain. None of us has a crystal ball so we had better keep Trident just in case. He points to the dangerous escalation of tension by the Kim regime in North Korea and Iran’s suspected nuclear weapons programme as justification. All well and good, until you scratch beneath the surface and realise what a highly contingent argument this is for the economic, political, opportunity, and moral costs at stake (yes, moral, because the practice of ‘nuclear deterrence’ rests inescapably on the threat of use – the threat of indiscriminate and catastrophic nuclear violence).