Progressives would not hesitate to use militarized police to suppress their opponents.
Progressives would throw conservatives into the cattle cars.
Agreed.
A militarized Civilian Security Force that is just as well organized, just as well funded as the military will be used exactly in the manner you fear.
Why do you think the Tea Party and Conservatives are demonized like they are? Once a government and ruling class of a society demonize a group and segment of their population, without exception that leadership embarks on an effort to eradicate them.
And on this very board you have Conservatives rationalizing the need to have domestic law enforcement better equipped and armored with military grade hardware than combat troops we sent into Iraq.
What they support today in putting down a bunch of feral gibmedats with a military force, will end up being used on them tomorrow by those who will declare them a threat to the state.