A person can be killed instantly through many different means. Gunshots to the brain, being crushed by immense weight, being crushed by smaller weights moving at high speeds, high speed collisions with hard surfaces.
As we know it, to be killed painlessly, is to be killed instantly.
If you instantly destroy a person’s entire brain then they died without pain.
Yet the most effective ways of instantly destroying someone’s entire brain are considered ihumane.
Like letting someone die of an untreatable disease but giving them so many pain meds they can’t feel anything is “humane” but shooting them in the brainstem or destroying the entire brain isn’t.
If instantly killing someone by smashing their head with a massive rock, or shooting them in the brain stem is inhumane, then humans only consider it “humane” if it doesn’t leave a mess.
Obviously I’ve left out a lot of different ways to die, be they slowly or instantaneous, but that list is massive.
But I’d much rather die messily yet painlessly than painfully yet “pretty”
Humans will die regardless of that ideology. They will die painfully and slowly or painlessly and quickly.
But killing someone as quickly as possible, regardless of how “horrific” is more “humane” than killing them slowly, or in a way that causes unnecessary pain.