are vegetarians more ethical by not eating meat?

[littleendian]

An argument that would "tickle my convictions", if you will, would be one that explains why I should put a negative value on eating meat, morally or ethically.

Would you put a negative moral value on eating another human without distress? If yes, then you have to look at the reason for this: If you (like me) would not eat another human being regardless of whether they are mentally retarded or not, then placing this negative moral value on the act has obviously nothing to do with intelligence. Now all that remains is an arbitrary and for me superstitious distinction that we draw between our own species and other species. We used to draw this line between human races, whites and blacks, between men and women, all with terrible consequences and practices condemed today. The logical next step is to extend this line to where there is actually an objective grounding in reality for it: Whether you can feel pain or not. How can I ask for a relatively pain-free life, and all of us do, and not award this to others who have the same interest?

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How do you mean? The only reasons for vegetarianism and veganism should be theistic?

Yes. What difference does it make to an Atheist whether or not they kill and eat animals? If they don't like the taste, that's probably the only logical explanation. Other than that it's arbitrary.

"Because I can" is a really weak basis for morality, and I hope that most Atheists wouldn't subscribe to it, after all it would imply that murder or rape are okay as long as they get away with it. There is a logic to human behaviour and -- yes -- also to human emotions that goes much deeper than conscious reasoning.