No doubt, the Indians engaged in the most brutal warfare imaginable, including massacres of innocents. I wasn't contesting that at all.
My question was specific to the claim of cannibalism. It wasn't uncommon for one tribe to accuse another of cannibalism; it was the most reliable way to get the white folks to help you take out a rival. The Europeans tended to believe the claims without investigation, and they went into the explorers' journals.
Anthropologists, most notably William Arens, started questioning accounts of cannibalism, and found that most were not corroborated by first-person eyewitness accounts or anthropological evidence. So for the last few decades, most historians and anthropologists have treated cannibalism claims skeptically, until supported by objective (or relatively so) evidence.
So that's the spirit in which I asked the question. And after checking a few of the articles Google turned up, it appeats that the Iroquois are one of the well-supported cases.
You’d think that they found the skeleton and remains of Jesus who had not risen from the dead. First there was disbelief then anger.
Back to your point, it is certainly understandable that claims of cannibalism got the white Europeans excited, since civilized persons had already rejected cannibalism for quite some time. Remember Idi Amin? Heh heh heh! That got em going.