The sad part is that with the wrong mindset, both of those are problems. You will get some on you. Every cop who has ever used mace/OC has been cross-contaminated. If you're inclined to just close your eyes and go fetal at the onset of a little pain, it can shut you down.
If you have a weapon to bluff your way out of a situation, which a LOT of people do (moreso with guns in the closet at home than with people who CCW, or with mace, but it does happen), the weapon is more dangerous to you than it is to your attacker. "I wouldn't shoot him, I'd just hold him at gunpoint for the cops." No, you're bluffing, and you should pray he doesn't call. I think this tendency is a lot less likely with pepper spray, since it is non-lethal, but some people keep the same mindset.
Before anyone raises an objection, I will say that these problems vanish when you have someone willing to use the weapon. The problem is that the will is not disseminated with the hardware...and in the case of a PD handing out stuff to scared people who had probably never seriously considered carrying a weapon before that day, this is a valid point to consider.
Mike