You crave meat for a variety of psychological and physiological reasons, but not necessarily because you're missing something that meat provides.
My argument for not eating meat is simple - why kill something for food if I don't have to?
I've been a vegetarian for 15 years or so, and would question your statement that finding non-meat protein alternatives is complicated.
It sounds like you're trying to make an argument that not eating meat could have long-term health hazards, in which case I'd argue that it's easier to prove that meat is bad for you than it is to prove not-eating it is.
Now, this is all anecdotal, I was just addressing that my body responded in a way that suggested that I did "require" the protein.
With regards to the more formal argument, I'd word it more that you put yourself more "at risk" for certain health hazards by cutting ANY core part of the diet out. It's certainly easy to prove meat is "bad" but most of the studies I had seen involved excessive consumption, which defaults back to the general statement of "all things in moderation". Do you have references that show the former (negative effects) without the latter? (ineffective dietary balance).
To summarize, I'd agree if we're only talking in extremes, that it's very easy to show that meat is bad. So I'd qualify all my previous statements with "a well balanced diet"
Mostly, unless you've developed some kind of novel purely-synthetic foodstock, you have to (well, you can probably get away with dismembering living things rather than killing them, in some cases.) To a certain extent, you have a choice about whether the "something" killed or dismembered is plant, animal, fungus, etc.