Here are the world's major religions ranked in order of dietary extremism:
1) you can eat anything, including dogs, but you're not supposed to enjoy it because life sucks.
2) you can eat anything except cows.
3) you can eat cows, but you can't worship them, and you can't eat tasty pigs.
4) you can't eat tasty pigs and you can't have dogs as pets either.
5) you can eat pigs, but you can't eat anything except fish much of the time, and you can't act like goats. And you can't eat dogs.
6) you can't eat any meat at all, only disgusting vegetables.
Only misguided, way-out hippie freaks join your radical religion.
About religions 2 and 3, I expect they have some common root in ancient prehistory, maybe the Indus Valley, and there was some great schism between the cow-eaters and the cow-worshippers that resulted in their hardcore opposition to each other on the issue.