I'm retired military, 21 years. You might be surprised about how many discussions we had about turning our weapons against our own countrymen for political reasons other than preserving freedom when I served. Most of us would refuse or defect if we didn't think we were being given a lawful order! A "lawful order" is defined in the Uniform Code of Military Justice! The only catch was that if you refuse an order you better be right!
I'm so happy everytime I hear this from military personnel. I have heard it before but I fear that many will side with the government.