http://slatestarcodex.com/2014/07/30/meditations-on-moloch/ Is a very interesting illustration of it.
More population, more pressure on all ressources, more conflicts.
... but, my solution would not be reducing numbers, or birth control, but more and better technology to get more land and ressources available. Also, rich people are usually not rich on childs, they can't afford to feed. So let's build technology, that makes everyone rich ...
Once the oil is gone, much of that population will soon follow.
The desire for money is rooted in a deeper problem. Money is just a means of exchange. What more money really gives you is access and opportunity. The more money you have, the more access you have to limited resources. We want more money because we don't have enough to own the things we want, do the things we want, control the things we want, etc.
Money is a means for control and fulfillment, both of which are not universally available due to hard limits (we don't have unlimited resources) and relative intangibles (the structure of society). A real root cause analysis would go deeper than "The love of money" to why money is something to be loved.