> There's no rational reason not to use dogs for meat...

Yes there is, unless you would make the same argument for having sex with relatives - which philosophers have rationalized against for thousands of years (way before the genetic consequences were understood). Morality is a rationalization. Dogs are genetically predisposed to be man's best friend - friends don't get eaten.

Diamonds don't even come close, there is no positive moral argument - just a fairly recent PR campaign.