Star Trek: 10 Dumb Decisions (That Characters Survived)

We're aware that Decker wasn't mentally stable during his tragic swan song on the original series, and this is the only example on here which does technically contribute to a later character death.

Nonetheless, it's strange and out of character that any level-headed senior officer would trust a traumatised man with command of his ship, and whilst Decker may sacrifice himself later, it's a minor miracle no one else died in his hasty and ill-judged phaser attack on the doomsday machine. Sure, Decker cited regulations in order to force Spock to hand over control, inciting Kirk's rage - but it's not like this would have been the only time regulations were ignored in The Original Series (including the Prime Directive, repeatedly) in the interest of the right move.

Fundamentally, it's a machine whose immense power we soon learn Decker should have understood better than anyone else on board, making this one an inexplicable move on Spock's part.