Point is, one should be able to not allow someone or something on their property for whatever reason they please.
It's not that I'm against guns, I'm just for property rights.
If you allow my vehicle on your property, you're violating my property rights by searching the vehicle. In other words, your property rights ends at my car door handle as long as you allow my vehicle on the property. If you don't like what's in your employee's cars, you might as well bulldoze the parking lot.
It's not the same as providing a locker for a worker. The company owns that locker and can search it.