At least he was also captured and sold as a slave. Moreover, Dio Chrysostom chose him as his anti-slavery champion in Diogenes or On Servants.
Diogenes argues that it is better not to have slaves at all, observing that:
… nature has made each man a body that is sufficient for looking after himself. — Dio, Oration 10.10
Be the man Marcus Aurelius thinks you can be