It has been argued successfully many times before, how many times does one need to be hit in the head to be justified in your expert opinion?
Mace is a force multiplier- it gives the advantage to the user over the target. Incapacitate, dominate, eliminate. The trained, certified, bonded Pinkerton Security Guard had no way of knowing what the rather large assailant would do after blinding the guard with a very large quantity of mace. Would you, as the security guard, wait to see if the mace user would be content with just spraying a large amount of mace? Look up 'agent of the owner powers', they give security guards more leeway than a LEO. I'm guessing the dead hefty guy got his 'knowledge' of Pinkerton Security Guards from 'Paul Blart, Mall Cop'...
Those on the rabid right like to chuckle about not fighting, resisting, disobeying a cop when the citizen is shot dead... why no chuckles now??? ✌