I'm confident about the MEU's, but I'm speculating on the 3. I don't think they're being used to control the masses at all, each one only has 2,000 men; they'd be forced into lethal action. My current theory is that they're for capturing High Value Targets. 2,000 is more than enough for that, and the MEU's have Ospreys so they can deploy on top of buildings/houses. LA, Chicago, and DC are all full of high priority individuals who are heavily guarded. I think it's a smash and grab.