That is exactly when it is the employer's responsibility. If they make a decision to not let employees defend themselves, that decision stands under all circumstances.
The employer isn't making that decision. YOU ARE.
If I state that you cannot come in my house with your dog, I am not depriving you of your dog. I am depriving your of the option to come into my house AND bring your dog with you.
The same applies to an employer. If you don't like the idea of being without a firearm, then don't choose to work where they aren't allowed.
Liberty is about having dominion over ones own property and also about making your own choices. You are only half-way to understanding that.
You have no right to dictate to another man what you will be doing on his property. You can only decide not to enter if the conditions are not to your liking.