All other human groups have made contact with each other in one way or another. What is the reason for keeping these people in perpetual isolation?

The Uncontacted Indians of Peru

~snip~
Uncontacted for good reason

Everything we know about these isolated Indians makes it clear they seek to maintain their isolation.
On the very rare occasions when they are seen or encountered, they make it clear they want to be left alone.

Sometimes they react aggressively, as a way of defending their territory, or leave signs in the forest warning outsiders away.

The Indians have suffered horrific violence and diseases brought by outsiders in the past. For many this suffering continues today. They clearly have very good reason not to want contact.

~snip~
Following first contact, it is common for more than 50% of a tribe to die. Sometimes all of them perish.

More:
http://www.survivalinternational.org/tribes/isolatedperu#main

What happens when an uncontacted tribe meets 'civilisation'?
Nina Lakhani
Saturday 04 February 2012


Margarita Mbywangy has spent her life fighting for the right to exist. At the age of five, she was kidnapped and sold into domestic slavery, removed from her family and the hunter-gather way of life that her Ache tribe had practiced in eastern Paraguay for millennia.

Ms Mbywangy spent the next 13 years known only as Margarita – the name chosen by her new "mother" who insisted she was her daughter, but never hugged her, didn't send her to school and made her cook and clean for the family. She looked and felt different; people in the street called her "Indo" – a derogatory term used to insult Paraguay's indigenous people – but she had no identity papers, just a name.

This part of her story is by no means extraordinary. In the 1960s and 1970s many indigenous children in Paraguay were kidnapped and their parents killed by government forces and farmers who wanted to develop the acres of forest, their ancestral land, where they lived a nomadic life, trying to avoid the threats of the "civilised" world.

By 1976, all the Ache had been forcibly resettled on small areas of designated land where they had to swap hunter-gathering for agriculture in order to survive. Many died trying to defend themselves and the forest; many more died from new diseases such as flu because they had no immunity to these common conditions. The land was sold to farmers, roads were built and the valuable timber harvested. Only 36 families survived the slaughter. The government was accused of genocide.

More:
http://www.independent.co.uk/news/world/americas/what-happens-when-an-uncontacted-tribe-meets-civilisation-6358885.html

They'd be able to catch illegal loggers asap.