I done some readin’ on this a long time ago.
The Narragansett and Mohegans {SP?] were allied with the colonists, and loaded for bear against the troublesome Pequots....revenge for the predations of the Pequots on those tribes.
The colonists were horrified by the brutality of the allied Indian tribes: having subdued the Pequots, the colonists could only watch as the executions started. Written accounts exist of how sickened many of the colonists became at the slaughter. And, IIRC, the remainder of the captured Pequots were sold into slavery by those colonist-allied Indian tribes to other Indians. I recall no mention of colonists being involved in the traffic.
No doubt you are correct. During the French and Indian war the French could not always keep their Indian allies controlled after they won battles and slaughtered the defeated English and colonists.