It's a combination of: 1. Slaves were thought to be sub-human, and people largely didn't care about a handful of them dying. You don't have to go back all the

It's a combination of: 1. Slaves were thought to be sub-human, and people largely didn't care about a handful of them dying. You don't have to go back all the way to ancient Rome to find that attitude among the general public. Many highly civilized societies as recently as 1800-1900 felt the same way. 2. A lot of gladiators were willing professionals, and had chosen the career with the risks in mind.