Right, say we all suddenly stop eating meat. Every one of us. What happens to all cattle etc? They don't magically start roaming the countryside in some cartoon animal utopia, people won't make any money from them any more (As they won't use animal skins etc for anything) so they won't be around at all. No farmer is having fields of animals for the sake of it, next to all domesticated farm animals will cease to exist. So instead of saving them, they'll doom them to zoos at best.
This is a very naive view.
Considering the practices of industrial farming it would be better for most of these animals had they never been born in the first place. Certainly I would rather never be alive than be taken from my mum and trapped in a space barely larger than my body for the rest of my life.
That's not even taking into consideration all the male chicks and calves which are killed immediately.
I'm not even a vegan but I'm aware it's quite obviously the more ethical choice.