I think that's the scary question for a lot of people. Many ignore it, some like to embrace violence like they've discovered something new (instead of old), and to show how edgy and dangerous they are.

We all have good and bad in us, we are biologically the same as those Romans, and as all the people who do good things. We can choose, and we can bring out the good (or bad) in each other. Look at the society we've built, where such things are unthinkable.