I think the point the OP was trying to make is that WalMart, like any other public business does not have a measure of security if the public is allowed to come and go at will. And you could replace WalMart with any other retail business that allows RVers to camp overnight in their lots, like Camping World, Cracker Barrels, and even Freightliner and truck stop parking lots.
RV parks on the other hand are usually more secure feeling than an open parking lot somewhere. While there are no guarantees anywhere these days, being in a wide open public area is measurably less safe.