Question: What should society do for “uncivilized cultures” like the Sawi?

The concept of society has always bothered me. It is singular, but is always overflowing with intense disputes. Society is composed of many people, each with different ideology and belief. It is merely impossible to come up with one solution for an issue, such as what to do for ‘uncivilized culture’ like the Sawi.
Most readers of the novel, Peace Child, will support the actions of Don Richardson, transforming the culture when it is considered immoral. Such ideas are from our own laws, which states that no human shall kill other human.
On the other hand, there is the relativist point of view. People of such point of view will argue that Sawi are practicing their unique culture and should not be disturbed by our ideology and we should even try our best to preserve and appreciate their unique culture. Since the idea that Sawi should not kill each other is based on the Ten Commandments, which the Sawi were not even introduced to, the Sawi do not have to follow them.
These two arguments are so contradictory that reconciliation seems distant. However, I believe that there is one solution for the dispute. What if we let the Sawi decide? What if we only introduce the Sawi to our ideology and let them decide whether or not to fall under the kingdom of God? Upon observing closely, we can realize that this is what Don Richardson had done. He did not force the Sawi to believe in God nor tried to ban the practice of cannibalism, waness, and other immoral cultural attributes. Rather, he spoke in the words of God and gave the Sawi the chance to transform into holy figures. The Sawi ‘decided’ to conform to Don Richardson. The Sawi ‘decided’ not to believe in aumamay, not to take revenge on other tribes anymore, and ‘decided’ to please God in their actions and words. This decision has created all the changes among the Sawi society.
Our society should not force other society to change, nor just ignore their immorality. We should solely open their eyes to the moral and immoral, and ultimately to God. However, we should always leave the room for the ‘uncivilized’ to choose whether they want to accept Christ or ignore His presence.