why is eating meat is unethical? Or why is it ethical?!

Bring up the idea of "conditional compassion" in your debate. Would we treat "farm animals" differently if they could communicate to us in human language? Is human language the determining criterion for what deserves compassion and what does not? Is "conditional compassion" compassion at all? Do "farm animals" exist to produce food for us? Do they give us permission to kill them?

That depends on the person. I believe there is nothing wrong with eating meat. Someone else might not think the same.

The reason I believe there is nothing wrong with eating meat is because we have to eat it to survive. Ok, not everyone has to, but that's because they have money and fully stocked Mega Marts full of food. Take the Mega Mart away from them and put them in the same situation people were in not even a hundred years ago and they would have to eat meat or die. Eating meat is natural, humans are omnivores, and there is nothing unethical about it.

Would some of these animals even exist if they were not to be eaten?

During the course of evolution would we have cows, sheep, pigs, chicken? Maybe, but not in the numbers they are now.

Is it better to have lived and been killed for food, or not to have lived at all?

Plants and vegetables are living things too, as are fish. They are also grown to be used in food. People have no issue with eating those living things but they have issues with eating other living things.

In my opinion, there should be a moral concern for the environment. Over 90% of the meat we consume comes from factory farms which are polluting the planet like crazy and using up most of our resources. Forest are being burned to make room for grazing cattle. We need our trees to turn carbon dioxide into oxygen. How are we all going to survive in a polluted and dry plant? We need to work on our priorities.

I'll answer your question with two questions:

Does a non-human animal have LESS an ethical interest in not being owned as property or killed than does a human?
Does a non-human animal have LESS a right to have that interest protected than does a human?

If yes, why?

Malteseken, if you're honestly likening sentient creatures to non-sentient ones,
you need more eduction in philosophical ethics.