I suspect that the reason the Security company does not promote OC (or any carry on duty) is two-fold.
1. They have liability issues and to have someone working for them who can carry a firearm, it usually requires a higher level (such as off-duty LEOs), with higher need/risk;
2. The primary duty of most security guards is to observe and report and not to engage. The only time they'd engage is if the BG tried to keep them from reporting/leaving.
My opinion from some reading. So, I don't think you'll be able to give them your viewpoint, though valid that it may be, and have them capitulate on the policy. You'd have to demonstrate need, i.e. regular assaults on guards, or something. Good luck in your quest.