To be fair, sometimes it's the other way around, some right wingers use some other example of slavery from history, barbary pirates, early white slaves in America, or whatever, to argue against leftists somehow. I don't particularly think it makes any sense when they do it, but they do.
I suppose it's a bit like this, if you are white, you should still be 'woke' to the fact that you can be in effective slavery quite easily and that is how most of your fellow white people probably lived at some point, as peasants in some lord's estate or worse.
Does that mean you should be against coloured people? Not really.