The Sentinelese people, living in the stone-age on their island, want to be left alone but they have to learn that killing anyone that comes near them - even with good intentions - is not on. I have a humane and environmentally friendly solution to this problem: Tigers.
There are many zoos in nearby India, liberate six Bengal Tigers and release them quitely onto the Island via helicopter: after a few weeks of maulings and death, send in people with tranquilizers (or .375 H&H Magnums) to solve their issue and prove to them we mean well.
It doesn't involve the use of gas or napalm, it's a natural solution to the problem. I think they'd learn respect if we secretly released Tigers among them and then rocked up and killed them off. We might have to coax a few down from trees afterwards though.