What I am against any assumption that they are not capable of thinking it through for themselves. They might like (as some Brazilian Indians do) to stay, and they might like to leave. I would reject any argument (which I'm not sure you're making) that we should avoid contact for their own good. There is much bad in the slums of Lima, but there is much bad where they are too.
Modernity is no guarantee of anything, but it gives you possibilities the jungle doesn't, and the jungle at least is there as a fallback. Leaving them as untouched zoo animals, it seems to me, shows them no moral respect.