Not to justify any of this business, but why on earth wouldn't they apply 'beyond reasonable doubt' in their own minds when summarily executing somebody in the first place?
Because everyone hides behind "just following orders" up the chain.
It is also somewhere along the line of why police feel it is okay to try to shoot suspects on a busy street and often shoot the wrong innocent person and mess up their lives.
That sort of standard works when the executor has massively more power than the executee. For the US versus an ordinary criminal, we can do it. Facing something that looks more like a war, applying standards of justice generally results in losing.
In this case, the executor has more power than the executee. The US can reduce people to bloody smears from drones that are almost invisible to their victims, with all the actual humans safely ensconced in bases hundreds of miles away. The people they're targetting have nothing like that - they cannot fight back without putting themselves straight in the line of fire.
It is also somewhere along the line of why police feel it is okay to try to shoot suspects on a busy street and often shoot the wrong innocent person and mess up their lives.