Devil's advocate..

[Aoi Magi]

Because a death-penalty is still more humane than chopping off hands and crippling someone for the rest of their lives.

Are you sure? That's a whole different post right there....
You can see your kids grow up, feel pleasure, eat pineapple, see the aurora borealis, enjoy comedy, sexual pleasures etc etc. all without a hand, or be dead !

It's not so easy. Death penalty is offered only to people in extreme cases where they are too dangerous to be returned to society. But for theft and such, the punishment still offers them a chance at redemption, a way to get back to a normal life later on. But if you chop-off their hands, you are not only making them a cripple, but also branding them a criminal for the rest of their life.