I reject the notion that that is the right thing.
Life expectancy in a tribe like this is often 35 years or less and are very brutal, expecially to those who can't fight to defend themselves. Civilized society cooperates so that we can ALL have better lives. The right thing to do is to invite them to join civilized society and to defend the human rights of individuals who wish to do so.
Typically, the people who want to maintain the isolation are the ones who control and brutalize the others. (i.e. Same as the socialist/communist model.)
You mention that their life expectancy is 35 years or less by your estimation. Well, exposure to modern society would do nothing to improve that. It is not as if exposure would suddenly have them living in modern American suburbia with access to modern medicine, proper nutrition and healthcare, and a real outlook for the future. No, they would simply be another poor Indian outcrop living in the outskirts of some slum. Looking at life expectancies for poor people in the favelas of Brazil (and these guys would be so poor they would not even be staying in the slums ....they would be too expensive), there would be no measurable improvement in life. Also, talking about brutal existence in the jungle ...well, the slums of Latin America are harder than those of Africa. In the jungle the main worries are exposure to the elements (they have lived in the jungle long enough to take care of that), lack of food (not a problem in the amazon basin which has enough grain fruit and game), lack of water (again, not a problem in the Amazon), hostilities from other tribes (this is not the problem that movies make it to be ...the only place such conflicts were big was in Papua new guinea during the times of headhunting tribes, and even THAT was not as bad as most people believed. most battles were primarily ceremonial, with the real killing and head hunting only happening when decorum broke down and ceremonial wars could not suffice). Obviously there are predators (e.g Jaguars) and dangerous animals (e.g. several species of snake like the Fer de Lance, as well as other animals and insects that are not necessarily benevolent) but then again, it is not as if every day Jaguars take humans. Most predators avoid human settlements. Thus it is not as 'brutal' as some may make it to be.
Modern life, on the other hand, will be killer for them. Unless they have a standard of living that is very high (impossible for people with NO skill sets that are applicable to modern life, apart from women who have sexual organs, and men who can take up cheap labor as loggers at wages lower than the poorest man from a favela), that means that modern life would actually be worse than what they currently have in the jungle. The fact that the tribe is still thriving (and must have been in that general area for centuries) means that they are functioning alright. It may be a different lifestyle from ours, but they have been functioning. What does modern life have to offer them apart from disease, exploitation, and social ills? After all, it is not as if after their 'discovery' they will be given decent housing (it will not even be decent by Latin American standards) and running water.
If modern life meant that they would actually have a modern life, then I would be all for their introduction into our world. However, based on other 'discovered tribes' over the last 5 decades, all that will happen is a disease-shock, sexual and wage exploitation, and a level of poverty that is grueling even by South American standards. A good portion of them will die quickly due to disease-shock, and after the initial media publicity the rest will simply fade into the dregs of society.
Honestly, they should just be let to be. Bringing them into modern society will be the worst thing to happen to them.
Final thing ...you mention that the 'right thing to do is to invite them to join civilized society and to defend the human rights of individuals who wish to do so.' Please remember that they are not being discovered in some advanced Western capital where human rights are held in esteem and there is some sort of blanket that tries to take care of the most basic needs of even its poorest members of society. These guys are being discovered in the Amazon, and in Brazil if you are below a certain economic threshold it is really a dog-eat-dog world. They have NO skills whatsoever to cope with a modern society. There would be no one to 'defend their human rights,' and they would not be seen as individuals but rather as quirks (for the first couple of weeks) before being forgotten by the media, and a year or so later a portion of the tribe would be dead due to disease-shock, and the remnant either working as bottom-tier prostitutes or cheap-@$$ labor. That is the story of 'discovered tribes.'
The only option would be for the government to set 'ethnic centers' where tourists pay to come and see them living in their 'natural habitat,' which is basically another name for a zoo. That is the BEST CASE scenario for them.
Thus, unless Warren Buffet decides to put money aside for those people that will be used as a fund to take care of them in the modern world, those guys would be dead ducks amongst us. They would be as out of place here as we would be in their environment. No education, no money, no economic skill-sets in South America .....that equals an early death for the lucky ones, and a hard-as-nails life for the unlucky ones who don't get taken out by chickenpox (you should see what the relatively benign chickenpox does to an adult with zero immunity, and let us not get started on the flu, measles, whooping cough, the diptheria and cholera that run rounds amongst the poor of Brazil, and all sorts of other stuff that is anathema to the system of a tribe that has lived in an encapsulated micro-system for centuries).
A life hunting peccaries and birds, and eating berries and grubs, is better than living a level below the type of life to be found in a Brazilian slum.
Actually, I’d give my one life for your right to disagree, but you sound as if you’re the one who wishes to impose strictures upon an independent people and I cannot agree with that.
If you can prove that they are being enslaved or coerced in any way, can you prove that it is not just natural selection and survival of the fittest, as well as their chosen method of “governing” their society?
Unless you can prove that these people have killed off millions of their own kind to enslave them, as civilized peoples have done for centuries, I will stick with my premise that it is best to leave them alone. Hopefully they will fare better than we civilized humans.
It is far better therefore, to make contact and introduce measles or TB or flu.
Instead of 35, the life expectancy curve approaches 0.