How much meat individuals choose to eat doesn't just affect those individuals, though. It affects everyone.
Should we be free to heinously pollute the planet? Because raising livestock is pretty good at that. Some argue that they're worse than cars in terms of their emissions -- not even counting the water pollution resulting from livestock. We already have limits on pollution of many kinds, and most reasonable people agree with limits. I don't see what's unreasonable about limiting livestock emissions, either, even though we don't do that. Which means, as an answer, sure, individuals should be free to choose how much meat they eat, provided they can find that much and afford that much.
But society as a whole clearly needs a limit on that.
As for the source, there's a boatload of them in both directions, it appears. Real contentious, as some say "
we're already past it" and others say "
we could feed 10b with what we have right now if everyone was a vegetarian". Many more other differing opinions, like what Endus posted about extending our current systems.
Personally, I don't think the "west" is likely to see much of the increase that's going to get us to 10b. Nearly all of the countries with the high growth rates are developing nations.