"There WAS a widespread awareness during Newton's time that slavery was NOT ok. There were plenty of folks speaking out against it."

That's true, and as I already pointed out it was another century before slavery was abolished - so maybe that awareness was not as widespread as you suggest.

Again, if you want to do something about slavery NOW, instead of picking over what happened 200 years ago, google "human trafficking" and find an anti-slavery organization you'd like to support.