Honestly this is a very interesting argument. We can all sit here hundreds of years later and say that this was all wrong but then the world we know would not exist. This brings up so many unanswerable questions about morality, history, and philosophy. What is even the point of discussing such things? The only reason I see for judging the morality of historical actions is so that we can make better decisions in the present. So yes, the vast majority of Americans benefit from this genocide, but that does not make criticism of it irrelevant. What it does mean is that we should take no satisfaction or moral victory from criticizing history. As for Jackson's point in his own time, it isn't really asking this question. The point is actually to argue that this genocide has been and will continue to be worth it. Jackson is saying that if he was sent back 150 years he would do the same thing as the forefathers. It is worth noting that this argument reframes the conflict, shifting attention from the possibility of better treatment in the future to justifying past sins. It thus implicitly argues that destroying the natives is fine.