Ame, let's say you have left me no choice but to shoot you. I know, unlikely, but just for the sake of argument.

*holds up a Taser in my left hand*
*holds up a .45 in my right hand*

Choose, but choose wisely.

Seriously, I would love to find a completely non-lethal defensive device, I really would. But even in Star Trek, a repeated hits from a phaser set to stun can kill. Expecting a perfectly non lethal but perfectly and instantly effective wonder weapon is not realistic and never will be. "Non-lethal" is a myth, always will be. "Less lethal" is the goal people have in mind.

People have died due to allergic and sever asthmatic reactions from pepper spray and mace.

Various low-lethality projectiles can be used to kill, just aim for the head at very close range, even a blank can kill.

Batons can kill and maim very easily, anyone who's ever studied serious stick fighting knows that, or is just unlucky, particularly if someone is not able to feel pain or simply over powers you when you get close enough to try for locks.

Jabby-zappy stunners can't kill without some very odd circumstances, but do the the higher voltage if the planets are aligned wrong they are very easily able to do so- if they don't, someone can fight through them, and at knife fighting range...

And hand-to-hand requires a lot of training and isn't as effective against crazies and drunks as you might think unless you are willing to break bones and if need be kill them with your bare hands, because you have no stand off.

Realistically, the Taser is one of the best tools out there in terms of less-lethal, but it is only one of the ones available. There are ways in which it can kill. But I can kill and maim with my bare hands easier than I can with a properly applied Taser. If you are going to defend yourself, there is the possibility that only lethal force will work, or that the other guy is just unlucky and dies. That they might die is better than you dieing.