[ben_w]

The reputation of the Mayans was of large scale human sacrifice. As I am not a historian I have no idea how accurate this reputation is, but that reputation is a reason for thinking they were more violent than the average contemporary or later civilisations…

…although now I realise I have no idea how it compares to the mass burning of suspected witches in parts of europe.

[namaria]

Unjustified killings are still a thing. Are Mayans ultra violent but Russians not?

[ben_w]

Perhaps I've missed the news story about Russian soldiers cutting out prisoners' hearts as blood sacrifices to the maize god…

Regardless, modern violence is also condemned when it happens. Unless done by the in-group, then apologists try to brush it away as necessary for some reason or another. If your point was meant to be about the latter, I'd agree, though it didn't come across like that on the first reading — those sacrifices (and indeed the in/out group difference) are the "why" in "Why would you think Mayans are any more violent than other contemporary or later civilizations?"