These weren't Europeans in the rain forest (which is a large continent of many different peoples), but mostly Spanish and Portuguese. Who married and had kids with native Americans. They weren't racist as we think of it today, they just held little regard for human life, especially little regard for non-christian human life.
To put this in perspective, this period came right after 100 years of bloody civil war in Spain that produced some of the most efficient killers the world had ever seen.
[EDIT] I shouldn't have said that they weren't Europeans, but that not all of Europe was represented, only Portugal and Spain. That blaming Poland or Germany for the activities of the Spanish was pretty unfair.
The Dutch controlled large parts of Brazil throughout the 1640s and 1650s, the French had substantial settlements in present-day Guiana and attempted to claim parts of Brazil as "France Antartique," and the English had a number of failed colonies in Amazonia and the Rio de la Plata as well. Heck, even the Scottish attempted to settle a colony in the Darien in present-day Panama. And that's not even including all the buccaneers and slave traders of various nationalities. I'm not interested in wading into the parent discussion, but just wanted to point out that colonialism in Central and South America really was a pan-European phenomenon.
Edit: also worth pointing out that the Spanish monarchs for the period we're talking about were the House of Hapsburg and hence claimed extensive territories in what's now Germany, Austria and Holland, so even many land-locked European regions were involved. There are a surprising number of Iberianized German names in colonial documents from Latin America.
To put this in perspective, this period came right after 100 years of bloody civil war in Spain that produced some of the most efficient killers the world had ever seen.
[EDIT] I shouldn't have said that they weren't Europeans, but that not all of Europe was represented, only Portugal and Spain. That blaming Poland or Germany for the activities of the Spanish was pretty unfair.