I've been sprayed by a variant of pepper spray (OC spray) and it will mess you up for a while. If there are protesters who are somewhere they shouldn't be, threatening others/law enforcement, or refusing to comply with legal commands, absolutely spray them. It's less than lethal and is extremely effective. And it being really effective is the reason protesters are complaining about it.
Protests can easily get out of hand and turn into riots or other dangerous situations. Pepper spray is an excellent tool for controlling crowds of protesters that is not lethal or particularly dangerous. It is a deterrent that can keep protests from getting out of hand. It is far preferable to use pepper spray than it is to use lethal weapons.
I'm not sure what the best way is, but pepper spray is better than truncheons, guns or tanks. If protesters become violent, I'd rather the police or military use non-fatal methods of crowd control before going right to guns and killing people. Pepper spay is a pretty painful deterrent, and isn't fatal.
Pepper spray, sonic cannons...anything that gets people off the highways and streets so we can all get on about our day is just fine. I mean, let's stay short of lethal force, but it is really boring having to dodge around protests over things like homeless camp removal and legalizing pot. Those don't deserve protests.
Protesters should not be "dealt with", especially if they are being peaceful. People have the right to protest peacefully, and should not have dogs sicced on them, water hoses sprayed at them, rubber bullets shot at them, pepper spray sprayed at them or arrested for participating in a civil and peaceful protest.
If the protest is non violent, then absolutely not! If it is violent, then it might be okay, depending on what they do. The one protest in UC Davis definitely was inappropriate, and I favor maximum security prison for all those cops who pepper sprayed for about 25 years, as well as the chancellor or having ordered such a barbaric act against her own students who were not even causing any harm.
Pepper spray is an ineffective deterrent. Protesters who are violent in any way are a actually domestic terrorists according to U.S. Code, and should be treated as such. Rubber bullets and tear gas should be used in excess. Violent criminals deserve no mercy from Americans. It has been shown that tear gas is a very effective crowd dispersal.