in biblical times a lot of what was described as slavery was just very serious contracts of service

the "slave" usually lived very well, had their own house and family, and ultimately did have the veto power over anything unreasonable

part of the proof of this is just look at how many times the word "servant" is used in place of slave

compare also the very concept of "lifetime employment" promises that many socialist governments gave to their servants... it's a lot similar... the deal is mutually beneficial, so the constraints are the necessary tradeoff