What got this thing started was a big multinational corporation decided one day to bring in some German Shepards to sniff around the vehicles of their workers. They "hit" on some of them, and those that had guns in them were fired. The Oklahoma legislature then (nearly unanimously) passed a bill saying that a company can't fire workers for having a gun in their private vehicle on company property. Other states legislatures are following their lead. (After all, isn't is the primary purpose of government to protect individual Rights?).
In my mind, it is no different than a company trying to put cameras in employee restrooms and the legislature trying to stop them.
In theory, the "free market" would take care of this, but we don't have a free market. We have a quasi-controlled economy (40%-60%) run by bueacratic planners in the govt and in big multinational corporations. (If you doubt this, look at the advancement of "political correctness" in major corporations).
Corporations have a terrible history in this country of abusing their power. They will certainly do so in the future if there are not basic protections afforded by the legislature.
If they had an employee contract indicating this...then those employees either had the option of finding another lot, finding another job, or, as they chose, to violate that agreement and then be responsible for the consequences.
I would not do what that company did...but I believe they have the right as the owner of the property (individual or company) to set the terms by which their own property can be visited, parked on, loiterd on, etc.
I agree whole heartidly about the shape of our free market society...but the answer is not to use the force of law when it is in our favor to disallow or abuse or infringe on other's property rights, even when we don't agree with them. And I believe that is what this is doing...but that is just my opinion.