You can tell a lot about a society by how it treats those it has power over.
Pretty much every society has treated at least some of those over whom it has power over very, very poorly:
Assyria,
Persia,
Greece,
Rome,
Han China,
Franks,
Arab Empire,
Mongols,
Ottomans,
Spanish,
French,
British,
Belgians,
Germans,
Swedes,
Norwegians,
Soviets,
Americans,
You think it is justified behavior because 'others do it'. Not sure that's how morality or judgement of societies works. The fact that your immediate response is to defend the behavior based on appeals to 'but others do it' not on the basis of actual morality just re-enforces my point.