And I disagree. But let me ask precisely what you think such corporate policies accomplish?? If someone is going to "go postal", do you honestly think a company policy of "no firearms in your vehicle" is going to stop them?? When they're willing to commit multiple murders.
First off, private property owners don't have to justify the wisdom of any legal restrictions they put on the use of their property. I'm not arguing the wisdom or lack thereof of such policies, just the right of a property owner to restrict the presence of firearms on his personal property if he deems it right to do so. I personally support the second amendment, own several firearms and practice with them regularly. But I support personal property rights every bit as much.