[grecy]

>What is the logic for reciprocity

I don't pretend to know, but I can think of a few possible reasons:

^ Do unto others what you would have them do unto you.

^ Educate foreigners about the realities of how their country treats other people (obviously many don't know, even the author of the article is seemingly clueless).

^ Change the policies of their home country (as you suggest).

^ Realize that for an American, $100 is not a lot of money, so it's a good source of revenue in itself.

^ Realize that Bolivia is absolutely, jaw-droppingly stunning, and any American traveling in South America won't let the little $100 fee stop them, because it's clearly worth it.