[joycian]

I don't know if it's useful to see it as a zero sum game. The sun is beaming practically unlimited energy out towards us (and a whole lot more that doesn't reach Earth but is still available eventually).

Even if it is zero sum: if we all stopped eating meat, we could pretty easily sustain ourselves. Putting it on population size instead of how that population behaves is not useful and frankly fatalist.

[armandhammer]

There's more than just food energy, though. Lots of things that we rely on for modern civilization and survival are finite -- the most obvious being petroleum / gas and various minerals + metals. Additionally, retrieving these resources is extremely environmentally destructive in ways which take centuries or millennia to recover from (we've already extracted the locations where getting at this stuff was easy and less destructive). It's a lose/lose situation.