Years ago my grandfather slept with a police riot shotgun under his bed loaded with rock salt shot (laced with Cayenne pepper) shells made by a buddy of his. That was considered "less than lethal" 30 years ago. Now they put you behind bars for even owning shells like that. Now instead you can buy rubber bullets, bean bags, slugs,flechette rounds, flares, buck shot, bird shot, steel shot, tungston shot, basically, anything you want in varying degrees of lethality and legality. That is the one reason why you can't beat a shotgun, it can do a bit of everything, nothing perfectly I guess, but it can do way more then any other firearm.

Anyway, I guess what I am saying is no matter what, if you use a shotgun (or any firearm for that matter) on another human you better be prepared to take a life, both for the mental aspect and the legal aspect. It doesn't matter if you are loaded with rubber bullets or depleted uranium rounds, if you fire the weapon for defense you are shooting to kill and you have a good reason to do that. Whether or not the person you shot lives, is an after thought to be sorted out after the threat is gone.