It takes more guts to let a snake live.
Got guts?
Poisonous vipers? Are you for real?
Not when you live in the desert and do not know where they might be lurking. I had enough trouble in the SoCal mountains, and from what my brother tells me, it is a lot worse in the desert, with them moving about to escape the sun and then come out to hunt. He likes to let his cats patrol.
Our family Weimaraner got bit on the nose from a rattler, I am not of the disposition to let them live.
You never know where you will come across one. They are not cuddly little Boa snakes, but stuff that will put a very serious hurt on you. Especially if you are hours away from an ER.
I smash centipedes for the same reason, though we have friends that would not think of harming the damn things.