I've actually given this a lot of thought. Since I don't believe in transubstantiation, it's not a problem for me. But if I did, I would still not object, since Christ explicitly told His followers, "Hey... EAT ME!" I'm squicked by consenting cannibalism (like those guys in Germany), but I recognize it as an ethically valid decision.

I rank these choices of food from most ethical to most unethical:

Sources that unambiguously consent (Christ, the Milliways cow, etc.)
Non-animal sources
Sources produced by animals (honey, milk)
Sources that might be considered animals (eggs)
Animals not believed to be able to feel much pain (bugs, non-fish seafood)
Animals that might feel pain and anxiety, but only briefly (iced fish, humanely slaughtered birds and mammals)
Animals that probably feel considerable pain and/or anxiety (veal calves, fish cooked while still alive)