There are still tribes of Native Americans who do not have contact with the modern world. Should they be told about medicine, sanitation, and agriculture? What about electricity, cars, and Justin Timberlake? Or should everyone avoid contact with them so that their culture can be preserved?
I think that it should be up to the tribe members themselves on whether or not they want anything to do with the outside world. Of course, for them to make that choice they would have to be contacted. It is unfair to them to be denied the very knowledge of all the comforts and conviences that we enjoy. Even after these people learn about modern ways of life, they might decide (and should be allowed to decide) to continue on as they are, just as Amish freely choose to do without cars and I freely choose to do without an iPod.
Suppose the federal government decided to preserve Fort Wayne's way of life and sealed us off in a dome. While the rest of the world gets holodecks, hovercars, and the cure for cancer, everything here stays the same.
Ultimately, a culture cannot be "preserved". Cultures are dynamic, not static. Cultures are enriched by interactions with other cultures. Why insist that one particular culture shouldn't be similiarly enriched?