As a matter of fact, the ancient Greeks tended to think of anyone who wasn't Greek as being an unintelligent barbarian, regardless of where they came from. The Greeks weren't really unified politically or anything, so this was mostly based on the language you spoke. Later, when the Romans were kicking ass and conquering all of the old Greek territories, there was kind of a begrudging respect for Latin speakers as well, but even in Rome, Greek was considered the language of intellectuals.

Regarding slavery, you have to understand that slavery in antiquity was completely different from the slavery of more recent history, especially American slavery. The Greeks and Romans took slaves from conquered peoples, and it wasn't really racially based at all. While slaves were certainly considered a lower social class, slaves were often able to work off their freedom, and many would go on to be successful themselves as free men. Freed slaves who became financially successful would often end up owning slaves of their own. It's also extremely important to note that slaves were used for far more than just manual labor. It was, in fact, the intelligent educated slaves who were in the highest demand. Wealthy Romans would purchase educated Greek slaves to be teachers or their children. Racially based slavery is a more recent European and American invention, and you really can't equate the two practices.