Very true. I agree with you, but with regard to the Greeks and Romans, the problem was that they had a very limited view of who qualified as a "person" under their law. Slaves and members of other lower orders weren't considered legal people, which is what led to the famous slave rebellions.
Judaism, however, regarded any Jew as a person. Obviously, there were class differences and there were certain heirarchical differences in families (those who were priests and those who were not). However, the reason that somebody like Jesus - who was a nobody - could go into the Temple and teach was that he was a Jew. Obviously, the "regulars" at the Temple, who were probably well-off and considered themselves scholars, were a little annoyed by this. But they couldn't stop him, because he was a Jew and therefore a person.
What Christianity did was extend this to all of humanity.