Slavery as it was then was quite horrific and quite wrong by our moral standards
Part of the Israelite practice of slavery included a systematic destruction of any ties the slave may have had to their home, along with steps taken to essentially indoctrinate them into Israelite society. It's noteworthy that this practice of cutting all ties to anything outside the group is similar in intent to the Witness creed and practice of isolating its members, creating in them a sense that the Witness group is the only true family. It creates a dependance on the group, particularly for young members who are denied the chance to develop normal social interaction skills.