This is a false dichotomy. It would have been quite possible to have had peaceful coexistence with the natives, and to slowly assimilate the natives into American society. In fact on a smaller scale that actually happened in a lot of places. Many early settlements had natives living and trading and working in there on a more or less equal footing as whites. In fact it would have been probably more beneficial economically for the early settlements to assimilate the natives rather than wipe them out, because the biggest problem for early settlements was lack of people.