system
Given the following post, respond as if you're commenting on Reddit:
human
[40K] So is eating Xenos okay?

Respect for human life doesn't really seem to be a thing in the setting so much as respect for the empire. You also already have cannibalism to begin with in some of the imperial guard with corpse starch. 

So are there any moral quandries regarding roasting an Ork leg for dinner, or Eldar ribs in the slow cooker? 

No point leaving the bodies, to waste, right?
gpt
Strictly speaking, it's morally fine. Xeno lives have no value, but their deaths can still be of service to the Emperor.

That said, there are reasons why it wouldn't be a good idea to eat certain xenos races. Orks are liable to give you the mother of all fungal infections, Tyranids are loaded down with horrifying toxins and require an exceptionally skilled chef wearing full biohazard gear, and Eldar meat is pretty much tasteless so unless you've got plenty of barbecue sauce you're better off not bothering.

Tau, on the other hand, taste quite like chicken.