Sacrifice should imply taking a life in an act of humility/service toward one's deity. I know you technically can sacrifice any old corpse you see laying about...in my opinion that's weird, creepy, without value, and not what I'm talking about (nor do I think the command should be used that way).
With what I feel sacrifice should be, I can't see an argument against making it across the board evil. I think all of us are perfectly aware of cultures/religions that sponsor such acts today or throughout history..
But DnD wasn't created with cultural relativity in mind. It was created with a modern day, western, moral compass. If we try to take everything that was ever viewed appropriate from every human culture that ever existed...it's just something not worth proposing.
DnD is fantasy with modern day western morality. Killing a living being for sacrifice is evil.