"Subject" doesn't necessarily have to mean one who is ruled over. If someone is being investigated, they are the subject of the investigation. I think it's fair to say that the police were, at least, sent to investigate. If you're taking a class, you are studying a subject. If you are doing some sort of experiment, you may have subjects of the experiment, which may be people. It's not automatically negative, though I agree that it can be. In the way police use it, I think it's pretty neutral here. Instead of "this guy," or "the armed individual" or "the person who was just pulled over for speeding," all of those are abbreviated to "the subject(s)." No harm, no foul.
I am NOT making excuses for the arrests of lawfully armed citizens who have done nothing wrong. Just chiming in on the subject subject.
