We live under constant threat of sudden destruction via nuclear war. It wouldn’t take that many warheads falling on major cities to darken the atmosphere — making the consequences of even a regional exchange (or the payload of a single ‘boomer’ sub) global, and potentially a threat to the integrity of human civilization. The control systems carry a frightening risk of malfunction, particularly in a crisis when nuclear-armed forces may be out of communication with higher level command and at immediate risk of nuclear attack.
The only safe option is to disarm as a global community — spare everyone the costs of the nuclear arms complex, while greatly diminishing the total severity of potential wars.