The DC snipers took advantage of the differing jurisdictions, and their rivalries. Until, of course, it became obvious that they weren't going to quit. Suddenly, co-operations was the name of the game, and the snipers were caught three days later. Now, again, the areas where they were operating make CCW impossible to have, and the Va, counties involved are just as bad. The people were virtually unarmed, and the snipers knew it.
Many SWAT Teams today have the operational authority to shut down cell phone towers. That wasn't happening in Mumbai. The idea is an old one, and has been used successfully.
Actually, bringing in a truck-load of machineguns, ammo, RPGs and their rockets, and grenades may be possible, but will require an infrastructurte beyond that of a small cell.
It's kind of interesting that we acknowledge that large scale operations are pretty much out of the question, but we allow the small cell the benefit of their infrastructure. Likewise, we hold the DC snipers as gleaming examples of terrorism, but they operated, once again, in areas where CCW was forbidden. They were mobile, to the point of having NO base, no rearming points, and no real impact on anything that any other criminal has. They kill as many people in D.C. in a week-end as the DC snipers did.
Were they even terrorists? Usually that is defined by the operation for a political ideology. The action must be to foment terror, and stir resentment against the government. Otherwise, every druggie in a drive-by is a "terrorist", as opposed to a criminal.
Carrying rifles is a wonderful idea, until you get stopped, or one of the less enthusiastic members of society see it. Then, who's the terrorist?
The fact that one is armed, at all, is much more important than what they are armed with. A .32 ACP in hand is going to go a lot further towards slowing down, or ending, such an attack, than a .500 S&W Magnum in the house, or in the car, while you're shopping.
The real places where such armament could, possibly, be helpful, is while away from population centers. There, you may well stumble upon a training camp, or a cell meeting. There, you will need some serious firepower.
In the city, who's going to be able to tell that you're one of the good guys? The SWAT sniper 100 yards away? The officer who rounds a corner, and finds you pointing a gun at him? The idea of CCW is NOT to aggressively hunt the perps. It's your job to find a defensible point, and hunker down, defending yourself from threats identified as just that. John McClain aside, none of us is capable of taking on a group of para-military terrorists, while miraculously avoiding getting blasted by the LEOs responding.
Do you need an M4 carbine to do that? Or, just perhaps, the pistol that you truly are able to carry?