We've treated recently to reports of limited mob violence in various parts of the US recently, and then this weekend we have reports of widespread rioting and looting in England in the London vincinity. At this point I really don't care about the causes of riots, root or immediate. The violence is not being directed against anything that could be described as a legitimate target of force. If mob violence can ever be justified, it is only against representatives of an unjust and oppressive government, not against fellow citizens. Likewise, looting can only be justified if it is directed against the resources of such a government and limited to the materiel necessary to maintain opposition to that government. Libyan rebels looting government armories is OK; London yobs carrying flat screens out of Marks and Sparks is not. Morality lecture over.
The best defense against a mob is not to be there, of course, and if you are caught up near one to leave the area. Sometimes this isn't possible; you're on Sun Tzu's deadly ground, or forced to defend a position such as your home or livelihood. In these cases, you might want something a little different than your sidearm. Classically, this is the shotgun's role. Not for nothing is a shotgun often referred to as a mob gun or a riot gun. The big problem in using deadly force on a mob is getting the survivors to realize that you are shooting at them. I would expect that a 12-gauge's muzzle blast alone is going to make an impression, and a blast of pellets may take down several rioters, something a single pistol bullet is unlikely to do.
This may be the role that the Kel-tec KSG would excel at. 14+1 rounds of 12-gauge ammo is a lot of mayhem, and the whole package is relatively compact, making it handier in closenquarters. Of course, as a tube-magazine weapon, reloading after that 15th shot is going to be tedious, and compared to any handgun it's unwieldy and heavy to transport. But I can't think of a much better choice for a riot gun among non-Short-Barreled-Shotguns.