When it comes down to it we can just agree to disagree on this point. I believe in a more intermediate future where meat comes from animals that, yes, while being bred for consumption, are happy animals that lived happy lives; lives which would be better than any lack of existence. I believe most meat eaters would realistically support this future as well - if not through their purchasing power then at least potentially by law. Lastly, I believe that getting to this future is through strong support of farmers who have already achieved it.
>Would you choose to be fed okay food, in a pen, until you were about 15, then killed?
This might surprise you but actually I would be inclined to say yes. I would absolutely chose that life over no life [1]. Have you raised farm animals before? They generally feel safer and less agitated in a "pen" of sorts because they view it as protection. They get to socialize all day - and don't usually have to worry about predators or food. Humans aren't motivated by the same environmental dynamics as cows or chicken.