It's an interesting case where the universalism of certain politically-inclined types clearly crumbles. To draw a comparison, I'm pretty sure most people would be aghast at the idea of an ethno-purist, isolationist Switzerland.
Part of the reason might be our romantic view of primitive tribes. For example, while I intuitively feel that their culture should be preserved, I've read enough material about primitive tribes to realize that the Sentinelese probably have some questionable practices.