a rose may be a rose, but the system of helotage in Sparta was not slavery. Many Greeks had personally owned slaves, whom they called slaves. However, the helots were Messenian Greeks--fellow Greeks conquered by the Spartans. They lived in their own villages and did their own farming and producing of goods. They lived in fear of the Spartans, who required tributes of as much as 50% of what the Helots produced. Failure to produce invoked sudden and violent Spartan action. While the soldiers of other Greek city-states were part-timers who were usually also farmers, the Spartans lived off the helots and could thus devote their energies full-time to drill and training for war--thus the famed Spartan proficiency as warriors.
When the Iriquois were under the tutelage of more powerful tribes (prior to the 14th century), they thought of the exact same system as "slavery". (That's just to let you know I am not alone in this thought).
The very same ancient Greeks we are both referring to felt that the exact same system as applied by the Celtic speaking folks in Bulgaria to the German speaking folks there was, in fact, "slavery".
Look, admit it, the Greeks were simply trying to whitewash this business of holding fellow Greeks as slaves. It's time to put an end to their hypocrisy and call it what was.