There are a couple problems with the notion of "non-lethal" weapons. First and foremost, nearly all of them can, under the right circumstances, be quite lethal. Hit someone in the right (or perhaps wrong) place with an expandable baton, pepper spray someone with a respiratory condition, or taser someone with a heart condition and you may very well kill them. As a matter of fact, many "non-lethal" or perhaps the better term is "less-lethal" devices require just as intensive, if not more intensive, training as a firearm to be both effective and non-lethal.
Secondly, the effectiveness of most "non-lethal" devices is somewhat limited. Even a taser can fail as I can know of an incident in my own community where this happened. In the particular instance, a police officer deployed a taser against a crazed individual wielding a chair. Unfortunately, one of the leads got tangled in the legs of the chair and failed to complete the circuit. To make matters worse, the suspect then grabbed the taser wires and jerked the taser out of the officer's hands. Much chaos ensued and it was only through sheer luck that the suspect was able to be apprehended without shooting him. This is why, even in the age of tasers and pepper spray, that police officers still carry firearms. The unfortunate fact is that the most effective means of stopping a violent attck are also the most likely to be lethal.
Finally, a "less-lethal" device does not have the same deterrent effect that a firearm does. If a violent criminal knows that his intended victim may be armed with a taser or pepper spray, he can be reasonably confident that he won't be killed in the course of trying to commit his crime and, while it may be painful, he may even still be able to get away. If he knows that his intended victim may be armed with a firearm, however, then he also knows that he risks his life in commission of his crime.
The notion that eliminating guns will make us safer is based upon the flawed logic that all guns can be eliminated, they can't. Even in countries where private gun ownership is completely forbidden, there is still at least some gun crime because criminals, by definition, do no obey the law. Even if banning firearms can reduce gun crime (and such has not always proven to be the case in the U.S. as evidenced by Chicago and Washington D.C.'s longstanding gun bans), that is only one type of violent crime. Rather than focusing on the tool that the criminal chooses, I think it would be much more productive to address the overall problem of violent crime.
Smith, and Wesson, and Me. -H. Callahan
Well waddaya know, one buwwet weft! -E. Fudd
All bad precedents begin as justifiable measures. -J. Caesar