Thus revealing what kind of people they were at the time.

Humans do the same thing to humans all the time.

We've banned and made efforts to eradicate: children out of wedlock, children who turn out gay, disabled children, jewish children, children who aren't "aryan", more than two children to a single family...muslims, christians, uyghurs, indigenous groups all over the planet, mongols...

And it's not at all a thing of the past as in just the last 50 years we've had ~15 attempts at the exterminations of targetted groups of people.