I mean, this is an ideological point. It's not based in reason, won't be changed by reason, and is really only a signal to end the engagement with the other party. There's no way to address the point other than agreeing with them, which doesn't make for much of a debate.
> an 1800s plantation owner saying "can you imagine trying to explain to someone 100 years from now we tried to stop slavery because of civil rights"
I understand this is just an analogy, but for others: people who genuinely compare AI training data to slavery will have their opinions discarded immediately.