Yes of course it's not ethical or good. But lou1306's point is that the Romans didn't think the barbarians were bad, but rather saw that the barbarians had some good stuff (land, fighting ability) and wanted to take that stuff for their own. That is, the Romans weren't motivated by hate or the desire to destroy, but by greed and desire for power.
Agree. Another issue, when discussing this topic, is that Romans are believed to have adopted the Greek culture after the conquest of Greece. This is indeed mostly true, but not when it comes to the attitude towards foreigners, which could not be more dissimilar.
Greek culture was much more insular. Greek poleis really considered themselves to be superior to anyone who did not speak their language (which is what "barbarian" actually means). And, while they did invest in colonies, they were never really interested in conquering territories where other cultures were already present.
Needless to say, this kind of attitude does not lead to burgeoning territorial acquisition.
Romans were much more aggressive and warmongering, but they also showed some degree of acceptance of the cultures they assimilated. They allowed provinces to keep some of their pre-existing laws. They were fine with people worshipping their non-Roman gods, as long as they also recognized the divinity of the emperor. And, as I said, they routinely employed barbarians at all levels of their society (not just for slavery, as it is sometimes assumed).
By today's standards, it is. However, we should not use today's worldview to judge another era's way of thinking. Also, a citizen was not just a "subject". A citizen from a conquered province could rather easily become senator [1], and some even became emperors (e.g., Septimius Severus was born in Leptis Magna, in modern-day Lybia, from a Punic family). Also:
> "they are now your subjects"
Nope, they were always the subjects of the emperor. That's the point of calling yourself an emperor. And it's not limited to Rome: the Persian and Chinese emperors also claimed their power to be universal.
[1] That was also true in Republican era. There's even a running joke in the Asterix comics series, where the chief of the Gallic village recurringly says that Caesar offered him a seat in the Senate if he surrendered.
The whole point of my comment is that it isn't just up to the emperor, claiming your power is universal has always been a douchebag move. Claiming much power at all for that matter.