I agree with Spock, also in that I do not have the energy to make long posts on this.
Just a few remarks:
* Before you talk about communism or socialism, you should find out what that really means. The basics of the theory. Not the so-called socialist nations that never really have been true communist or socialist states at all! Also, socialism does not have to mean that everything is owned by the state, but that everything, all resources and production is there to serve all people. The ways to achieve this are manyfold.
* The liebig limit. It should suffice to say two things - one is, we do not want to hit that limit. Yes, population will control itself to its limits, but no it wont be pretty. What makes it worse is, that we are facing actually a decline of that limit rather than hitting it from below, we will find ourselves suddenly above it, worsening the effects. We have two choices - voluntary reduction (my preferred method is also socialism and education, but I would not oppose a two-child policy to keep at least ZPG); Or involuntary reduction by random means. Now whcih of these could be more "humane" - hmmmm
* increasing the planets capacity. It is possible in some ways. Especially with enough energy. Desalinated water, Skyscraper farming and using modern farming technologies in some additional areas can increase output. The problem is, that more production never solved the matter of overpopulation. Each time humans devised better food production, population increased (Liebigs law) until all that benefit went to hell. And many of the modern aspects of increasing output are either harming the planet and ourselves or are not sustaineable in the long run (making the problem of living above the Liebig limit even worse)
* Eating less meat - same as before. temporary solution only. Eventually we would, like in "Avatar", all eat plant derived protein slurry and be able to sustain twice as much population but still be on the brink.
For those in this thread who think, that growth is not a problem and can be handled, maybe even by colonizing space, please invest half an hour or so into education and listen to a lecture from a mathematics professor at the University of Boulder who can explain the dynamics of growth. It is not a boring math lecture, I promise, it is very well done and obviously focuses mainly on the topic of this thread and the predicament on what solutions we could choose:
YouTube - The Most IMPORTANT Video You'll Ever See (part 1 of 8) (part 1 of 8)
Other than that all I can say is

:
and:

(translation: No, No, this is not communism; referring to the three self imposed communist leaders despite the fact that the mere concept of communism does exclude such a permanent position)
Oh and if you can understand German:
this is a great one-page comic on the neverending discussion on communism.