Some propagandists for atheism would have you believe that, in order to be truly evil, humans must be motivated by religion. This article provides convincing evidence — though vastly more such evidence could be supplied, from every era and every culture — that such insinuations are historically unsupportable and, indeed, blatantly untrue:
http://www.livescience.com/53615-horrors-of-the-colosseum.html
It was, in fact, only with the Christianization of the Roman Empire that the gladiatorial games and their associated violent entertainments were banned.