It's very simple almost every work place shooting is done by a current or former employee. If you push arming all of your employees-- then you have literally given the unhappy employee the ability to carry his or her gun into your workplace-- no, questions asked by the way. Think about how that will play out in civil court case about wrongful deaths???
Then who do you think is going to be liable when the rest of your employees decide to use their guns in the situation and shot up the place potentially killing innocent people? That's going to be another civil case you loose badly as a corporation that allows its armed untrained or poorly trained employees to go Wyatt Earp O.K Corral Style in the place. You're now on that hook too.
Anyway you slice this problem arming your employees and pretending that makes you safer and not open to massive civil liabilities is just a fantasy on your part. And it is also gives disgruntled employees the ability to carry their weapons into your work place further complicating the issues of labilities for workplace violence on your corporation.
So you want to add all of that liability to your company all in the fear that some mythical crackhead is going to come walking off the street to shoot up your landscaping facility? Please, man you're either paranoid or just a victim of lead paint chips....