Sacrifice and cannibalism were widespread among ¨new world¨ aborigines. Even the vaunted Iroquois would chow down on some of their brethren occasionally.
The Noble Red Man, eh?
There is no moral barrier to human sacrifice and cannibalism until the advent of what truly seems to be advanced Religion. If there is no single God-who-Said then there is no reason why not. Where there is a multiplicity of gods then some of them will require it because paganism is not about living a proper life; it is all about placating capricious gods some of whom are wholly Evil.