Plenty of people own armored and tracked vehicles. Some people even own tanks, although a tank with no working machine gun or main gun is sort of like owning a castrated stud bull.

If a person has enough money, they can own just about anything. If I own a nuclear weapon, have the ability to safeguard it, but never use it, who is harmed? The criminal aspect should be in the act not in the ownership.

Find the thing a progressive owns and loves and then threaten to have the government take it from them by force. I'm still not certain that they would understand.