Did Buddha oppose slavery?
Every Buddha opposes slavery. Slavery is ugly, it’s disgusting. Buddhas oppose even mental slavery, any form of coercive control people exhert upon one another with words and emotional manipulation, leave alone physical slavery which is one of the ugliest things humans have ever done.
Only an enslaved mind wants to enslave another. In enslaving another you are always enslaving yourself. If I want to be your master, in that I become your slave. If I need you to submit to me, I am submitting to that need. In the end, the master always becomes the slave.
When I am free, I allow you to be free. Your freedom is my freedom. We are either both free or we’re both slaves. There is no other way.