Is there any real reason to spare [spoilers]?

Is there any reason, both story and gameplay wise to spare Adam Smasher? The dude is just the worst, with very little redeeming qualities. There isn't really a moral angle to saving his life. Doesn't seem to be a gameplay reason for leaving him alive. I can't justify a single reason that V/Jhonny would leave the son of a bitch breathing.

People who did spare him, please enlighten me.