Obviously it was a good thing that it was banned, but I'm just wondering if it would technically be considered authoritarian.
As in, is any law that restricts people's freedom to do something (yes, even if it's done to also free other people from oppression as in that case, since it technically restricts the slave owner's freedom to own slaves), considered authoritarian, even if at the time that the law is passed, it's only a small section of people that are still wanting to do those things and forcibly having their legal ability to do them revoked?
Or would it only be considered authoritarian if a large part of society had their ability to do a particular thing taken away from them forcibly?
So you are trying to argue that slavery is a RIGHT? This looks like and argument of guilt by association. Authoritarian is seen as bad, by giving the abolishment of slavery the label of "authoritarian" gives of the idea that you want to associate it with being bad.
If having a law that restricts one’s ability to do something is “authoritarian” then any law is authoritarian, because laws, by definition, determine what behaviour is and isn’t allowed within a society. On that note, morality determines legality, not the other way around.
Slavery means that, if you're rich enough, you should be allowed to revoke the rights of others. This is refutable at so many levels. If someone were to "willingly" agree to give up their rights, then just you're just taking advantage of someone who was born in an unfavourable position and have no other choice other than to accept (and maybe not starve) or starve.