Why shouldn't we eat _you_ then?
in germany there was a case of cannibalism many years ago where a guy known by the name Armin Meiwes slaughtered and ate another guy called Bernd-Jürgen Armando Brandes. never got the panic around it given that the whole deal was consensual. other than that you know yourself that society comes up with rules to ensure its stability and survival. eating each other wouldn't fly well from that perspective.
If you remove intelligence (or something quite similar) as the criteria, what do you have instead?
<check-mate/>
There is also don't mess with the effectively most powerful species on the planet whose members have collectively decided that (for somewhat principled reasons) none of them should be eaten.
Any parasite, bacteria, virus, and especially prions spread much much more easily the closer the food is to your own biology.
Cannibalistic tribes have had issues with this in even the recent past.