I've been a part of a "berming and clearing" operation in OIF; we built perimeters around a series of towns/cities each between 30-50K people. Used dozers to build a big earth berm, then topped it with triple-strand wire. THEN we went through each on a cordon and knock, searching for everything of course but SOP is to first establish that the household is in compliance with firearms laws, and confiscate all excess. Marines have done this (active & reserve) as have the Army (active, reserve and National Guard) for several years now. This is not new training. They have all been rigorously trained in the exact type of police activity that is feared will spread at home, and perhaps because of this there are those who think that would be a good idea - worked there, should work here.
BUT it was not a lockstep event - the individuals conducting the mission hated it. It was a great imposition on Iraqi families which most Marines actually cared about, and very little juice for the squeeze. Many of my guys asked me if what we were doing was ethical (Chaplains get asked that alot more these days.) I had a hard time answering that one. But it gives me hope that if they were asked to do it in their home town, they'd have problems - in fact, most would say no based on my conversations.
The military is not brainwashed - with about a million patriotic self-sacrificing Americans in it, that would be hard to accomplish. They are being asked with increasing frequency to do or not do things that run contrary to their convictions, and they too have a breaking point.
Our society is producing at greater numbers young men and women with no orientation - no compass, no fixed point - who are willing to go along to get along. And they would be the recruits for a national security force, which I would be worried about. If you want to undermine the liberal agenda, take every kid you know shooting and talk to them about civic virtue.