Your company can not do whatever they want with you. But they can set conditions you must meet in order to use their property or accept their salary.
For example, they can tell you what clothes you can wear (dress codes), what actions you must take (crunching numbers, making sales, etc), even what you can say and who you can associate with (sexual harassment policies).
If employers were trying to throw people in jail for keeping a weapon in their car, I would oppose them. If they want to set conditions for using their property or taking their money, I will support their right to do so, even if their conditions are stupid.
I must have misunderstood you.
I thought you said you supported a company proclaiming what employees could have in their private cars on company paking lot property.