Be fair to the Indians. The pre-Columbian Americas consisted of two empires, a larger number of chiefdoms, and numerous independent villages and hunter-gatherer bands. Fixing the blame for the sins of the Aztecs (who praticed ritual human sacrifice, what I believe you are referring to) onto all Indians makes about as much sense as blaming the medieval Scots for the sins of the Byzantine Empire (same continent, different people). Naturally, liberals often make the same generalization, but in reverse (the Yahi were nature-oriented and environmentally conscious, therefore all Indians were *puke*). You are right that some Indian tribes and/or empires certainly were extremely brutal.
Not just the Aztecs. Many Indians west of the Mississippi practiced human sacrifices. Probably some of the eastern Indians did too.
Human sacrifices were a common feature in "nature religions". Not just Indians. Europeans practiced the same sort of rituals.