1) Very few people who live in the developed world actually face "starvation." They might be really hungry, they might need better food or more to eat, but these questions take on the flavor of "If stranded on a deserted island and your best friend died and there was no other food would you cannibalize his dead body." People will do lots of things if they are faced with actual starvation, including eating tree bark or boiled shoe leather, but since Top Ramen is less than 50 cents per pack in any convenience store in the United States, you are very fortunate that you never ever have to eat meat, ever.
So don't give me that crap about needing to eat meat to live, unless you speak English as a second language and left your home country as a small child due to war and/or famine.
2) Omnivores can eat lots of things, including junk food, garbage, and each other (as in, cannibalize one's own) ...this doesn't mean it's their ideal diet. Pigs and bears will eat trash and sea turtles sadly eat plastic mistaking it for jellyfish, but it doesn't mean it's good for them to do so. If you actually research this topic, our ancestors actually ate very little meat. Humans are notoriously bad hunters so mostly foraged and occasionally caught an animal. Agricultural societies did domesticate animals for their milk and eggs, but strangely enough, even those primitive humans seemed to have more ethics than modern people. I say this because if read the Old Testament in the Bible there's hella instructions on how livestock is to be cared for (and even about foraging bird's nests for eggs) - those "primitive" people were better at treating animals as living beings than people in our "advanced' society. What does this tell you? It should tell you that people felt guilt for mistreating those animals, taking their young, or consuming them at all. Our natural state appears to be that of you standing with a gun and unable to shoot a grouse.
3) Obviously if humans don't need flesh to survive it's immoral to do so. I don't see how this is even a challenging question. I also again want to address these sorts of far-flung scenarios you're propping up as ostensibly "thoughtful"...our ancestors also needed to kill each other to protect their tribe, their land, and their food supplies when faced with a more violent tribe that ransacked their village, but since we don't live that way war has become an instrument of greed and power rather than an instrument of necessity, and eating meat is similar.
