Best be careful using surplus headgear. Note that, in these riots, several of the more experienced thugs use kerchiefs and helmets to keep in the fray. That makes people wearing similar attire a target to a pee'd-off cop, or even an upset shop owner.
A good point I think they missed.
Explain how any rational human is going to be carrying a military style helmet on their person when they're caught in one of these spontaneous riots? Do you wear it with your business attire? Carry it in your hands? What? If you have it in your vehicle, why not just leave when you reach that vehicle? Or, stay in that vehicle?
That's another thing... most rational people don't even see a need for a helmet in most cases other than what we'd consider normal. Part of that other discussion I referred to... somebody said the helmet is only advisable if its user is set to defend a prepared fighting position. Most of us, outside a military organization, won't. (You know all those pics of IDF walking around with M-4's that go around the net? I've never noticed them carrying helmets either.)
Okay, so if you're in your vehicle, and you stay in the area, you can get your windows smashed in followed by a Molotov. The helmet won't help that, and obviously, neither did the car. Everything I hear says get out of there.
Another issue somebody mentioned was the weight of a helmet causing neck/shoulder pain.
Most riots have little danger from above. The rioters will seldom establish a presence on floors above ground level, where the goodies are.
Heck, instead of a helmet, why not carry a rifle? That way, if someone tosses rocks or bottles from height, the prudent survivalist would just shoot them. It will only take one or two dead rioters to make that a game nobody wants to play. After all, you can't steal a 72" flat-screen if you're dead, or seriously wounded.
Well, L.A. in '92... I don't think the roof-Koreans had helmets, but I've heard a good many references to their rifles.