True, but I bet this guy could afford one. Luckily, he didn't need it for this particular event.
I think his house would have actually had to of been vandalized or destroyed, and him or his family with it for that to work, though. I don't think the court would be sympathetic to gunning down protesters for mere trespass.
And exactly nothing stopped them from doing so if they wished? They were already invading the man's property, obviously attempting to intimidate the man's home and family, etc. Yes, gunning down unarmed protesters is usually bad. But it could have easily gone that route and he would have been virtually helpless even if he bought the best weapons, carried an improbable amount of ammo and had the finest training from anywhere on the planet.
The only thing that can stop a mob of savages outnumbering you several hundred to one is gunships, fixed defenses (landmines, claymores, etc) or a machine gun.
Know why there's as many heavy crew served weapons on the NFA registry as there are? Protection from unions. There is a nickname for the M2HB other than "Ma Deuce", it is "labor relations". Most folks are unaware of the terrorist tactics of the 1920's, 1930's unions. Arson, train wrecks, murder, etc. Coal companies didn't exactly stock up on US Army ordinance for entertainment. Their company goons knew they'd be corpses unless they had heavy weaponry to hold off mobs. Thankfully, BECAUSE they had heavy MG's, they were not often needed.
Do you think these SEIU goons would pull these intimidation tactics if they knew the average home owner could hold them at bay? Whether said home owners owned MG's or did not is kinda besides the point.
This is not a theoretical "What If?" exercise. The aerospace industry is well unionized. A certain well known union (well known for intimidation) sent two goons to a coworker's house when he was working for a different company. Two large well muscled "gentlemen" asking him why he dared to make anti-union comments and that for health reasons, he should stop doing so. My buddy was single and made stupid bank, and happened to own NFA weapons. He inserted the muzzle of a MAC-11 into the left nostril of the closer gentleman and escorted them off the property. They did not come back.
This wasn't 80 years ago. It was about 5 or 6.