I think it's important to recognize that the violence of gladiatorial combat was both legal and accepted in Roman culture, where as dog fighting isn't today. So

I think it's important to recognize that the violence of gladiatorial combat was both legal and accepted in Roman culture, where as dog fighting isn't today. So, it's a little unfair to compare the two as if they're equivalent moral issues. Of course that hinges on the fact that you accept that morality is a cultural construct and not absolute, which is a philosophical rabbit hole.