Well, when we're talking about human beings as targets, the legitimate civilian use is "stopping" them. Not killing per se, that's the remit of the judicial system.

Unfortunately it's very difficult to stop a determined opponent without using "lethal force", in the case of guns a maiming or deadly central nervous system hit, or causing them to lose enough blood (a large fraction of opponents, though, will stop combat upon getting hit the first time). There aren't any other practical options.

If your question includes hunting, I can continue about it.

For target practice, they don't need to be "lethal", and generally aren't used with ammunition designed for increased effectiveness in live targets. The exception is practicing for self-defense, you need at least some of that to be with service ammo for a bunch of reasons. Lots of government units buy in bulk where the price difference for service ammo isn't large and use the same thing for all purposes, which I'm sure saves in administrative costs and ensures no one accidently goes out on the street with less effective target ammo.

So you're saying that if handguns could stop without killing, then it would be ok to ban handguns that killed?

Hand weapons for the purposes of civilian self-defense, yes (they wouldn't be "guns" except in the loosest of senses).

"Set phasers to stun" and all that; a nice idea, but way beyond the foreseeable future.

Given how many people's lives would be saved, why do you suppose that we don't have more research into less lethal handguns? Phasers, perhaps not. But there are many other options.