That's absolutely untrue. It does no such thing. All it means that as long as you're acting within the norms of our times you're morally neutral. Who has ever aspired to that? "Are you a moral person?" -> "Well, you know. At least I'm not immoral. I just barely pass the bar lowest bar for that". The future will look back at people who pushed beyond that, just like we do today, even if even those people will be (at best) morally neutral on many other issues.

Bartolomé de las Casas, Martin Luther King Jr., Gandhi etc, all of these people are looked back upon with great respect because of their morality - but the truth is that none of them would seem like morally great people today. They stand out because they pushed further on certain issues compared to their contemporaries, not because their thoughts and actions would stand out compared to ours (other than that they would seem very backwards and immoral concerning a lot of things).

I think the mindset is valid but the people behind it are inconsistent, if your locale is being around indignous african people. Then killing and enslaving them kinda goes against the whole "act local" thing.

Thereby making them immoral by their own standards. You cannot export your sense of locality to somewhere else, i dont think thats how it works.