I don't understand why anyone would want to exist solely on meat, or solely without. They taste better together, in a nice stirfry perhaps.
As far as morality goes, plants are fairly closely related to animals, genetically, so whether you live on acorns and dandelions, or you eat chilled monkeybrains for dessert every night, you're still destroying a living thing to perpetuate your own existence.
Atleast an animal has half a chance to avoid their fate. Plants can't even run away.
At the same time, though, when you eat, you're also preserving and bettering your own life, and what's wrong with that?
Humans might not be the single best thing that ever happened to the planet's ecosystem, but we're sentient beings. We create a lot of cool things, and think a lot of cool thoughts, and if any species on Earth has a shot at turning a dead world, like Mars, into a green paradise, it's us.
Cows aint gonna do it. Dolphins aint gonna do it. We just might.
Humans are awesome. We eat animals because we kicked all of their asses, even though we're the weakest, slowest, blindest, and deafest creatures on Earth. We clawed our way to the top of the foodchain, and it took us a couple million years to do it, and now we can celebrate that victory with a nice juicy steak.
The fact that we even care about, and have conversations about, where that steak came from just proves how awesome we are.