Politely ask the employer for an exception. If the employer refuses, you can find another job.
Consider the scenario where you can't feed your kids on what an employer pays. Do you want the govt. to mandate a "living wage"?
Consider the scenario where the employer does not offer free health care? Do you want the govt. to mandate that ?
Consider the scenario where the employer does not offer free child care, or a 401 k, or flexible time off, or time off for kwanza ?
Which Articles in the Bill of Rights are you alluding to in your post?
What do company pay and benefits have to do with self defense? The right to self defense is inalienable and is not negotiable with anyone. Nobody has the right to say what kind of legal weaponry an employee can keep in his car on company property. Case closed.
Laws against having weapons in a car on company property will never stop anyone who wants to commit an armed felony crime from breaking those laws and committing this crime on company property. Criminals, by definiton, don't care about breaking laws. It's the law-abiding citizen who is hurt by this kind of law because he then cannot defend himself against the criminal.