A Bulletin reader named Ryan Alt argues in the comments to this roundtable that “it is very difficult to imagine [a nuclear weapon] ban [treaty] as anything more than wishful thinking.” Another reader, Keith B. Rosenberg, writes that one should “[n]ever make a treaty that will not be adhered to”—essentially, that the ban treaty is too idealistic to be feasible.

I’ll argue the opposite—that realistically appraising nuclear weapons and their dangers demands the negotiation of a ban treaty. What is overly idealistic is to believe that humanity, if it possesses nuclear weapons indefinitely, will indefinitely manage to avoid nuclear war.

This brings me around to the concept of deterrence, which my roundtable colleagues Joelien Pretorius and Polina Sinovets have debated. My own view is that the Cold War may have represented a golden age for deterrence—and that age is now over. The Cold War world was organized around two superpowers that each possessed tens of thousands of nuclear weapons, ready for use at any time. The weapons could be delivered using air-based, land-based, and sea-based platforms. Both sides were confident in the other’s ability to launch a second strike; this confidence deterred a first strike.

But the world has grown more complicated. It isn’t organized anymore into stable blocs around two superpowers—rather, power has become more diffuse and nuclear weapons have spread. In nuclear South Asia, relations between India and Pakistan are worryingly unstable. In North Korea, Kim Jong Un himself may be worryingly unstable.

Today’s leadership profiles in the United States and Russia are arguably no better. Donald Trump’s control of the US nuclear arsenal has rattled expert observers ever since he emerged as a serious contender for the presidency. Vladimir Putin behaves with increasing aggression, virtually daring the West to put its foot down.

Realist thinkers have traditionally portrayed individuals in charge of nuclear weapons as rational actors, capable of performing accurate cost-benefit analyses and responding sensibly to the reality that potential adversaries possess nuclear weapons too. Some realist scholars have argued that the world would achieve greater strategic stability if more states possessed nuclear weapons. But even realists ought to realize that most leaders controlling nuclear weapons today can’t necessarily be trusted to behave rationally.

A characteristic of nuclear weapons that distinguishes them from all other weapons is that the destruction they cause is irreversible. After nuclear war, no program of reconstruction could ameliorate nuclear winter. No human effort could remove enormous amounts of poisonous radiation from the environment. Is it unrealistic, then, to be alarmed about the current leadership in the major nuclear weapon states? Even realists ought to admit that it is not.

So is it realistic to wait passively for disarmament while the power to launch nuclear-tipped missiles rests with leaders whose rationality is in question? Or is it realistic to work toward disarmament, including through a ban treaty, so that no irrational leader can ever initiate a nuclear war?

Oh, don’t forget—once your leader presses the button, it will be too late to say “Oops.”