Thinking about the thread's title, I think it's more a matter of the human race constantly wasting resources on a daily basis and the fact that humans do not help each other out.
I'd agree that human wastefulness and selfishness is a huge part of the Overpopulation problem.
We have people driving inefficient gas-guzzling vehicles because they care more about how their vehicle looks or being big / spacious than conserving fuel. Public transportation is often stigmatized as a horrific ordeal that should only be endured by poor people (and to be fair, in many cities it is pretty inconvenient, uncomfortable, or downright unreliable at times). We're using a lot of land and resources growing grain, corn, and soybeans which could, (in theory) be fed to hungry people, but instead is going to feed livestock because well, lots of people like the taste of meat. And as you've mentioned, in many cases, we're throwing away perfectly edible food, for one reason or another.
I've worked in the produce dept. of a large supermarket for years. The amount of food we throw away every day is absolutely staggering. Of course, much of it is moldy, spoiled, or (in the case of juice, prepackaged salads, etc.) past the expiration date and you can't really expect people to eat this stuff, let alone pay for it. Since management tends to see running out of anything as far worse than having too much back stock, we tend to order more than we need and of course throw more away as a result. And in some cases, we're throwing away produce with minor imperfections like an apple with a tiny bruise because people are extremely picky. We do have a small rack where we can sell bags of ripe or slightly bruised fruits / veggies at reduced prices. This stuff sells pretty well as people love a bargain. Unfortunately management tends to consider this a very low priority so we don't stock it nearly as much as we could.
On the bright side, our company has recently started to have us separate our organic waste so that all of the store's "bad" produce, baked goods, and dairy products are supposed to go into huge dumpsters which will be used for compost or livestock feed. A lot of what we throw away is the "convenient" prepackaged stuff (pre-chopped veggies, sliced melons, etc.) which of course spoils quicker than whole stuff. Separating all the foods from plastic and packaging is pretty time consuming so a good deal of our organic waste still goes into the trash dumpster and ends up in the landfill. I guess it's still a small step in the right direction but still there's something very disheartening about seeing so much food, much of it perfectly edible, get thrown away.
So what's the solution to people being wasteful and selfish? Education may help to a point, but I don't think human nature can be changed easily. It seems that we need to come up with solutions that don't conflict with human selfishness (which is I think what DArtagnan has been getting at). As to exactly what that would look like I'm not sure. Giving financial incentives for doing the environmentally responsible thing seem to work alright, but of course someone has to pay them.
And capitalism is certainly not the ideal economic system as it always requires exploitation. Not everyone can become rich in a capitalist society because most of us have to do the manual labor and grunt work... The haves will always want to have more, while the have-nots struggle and fight over the scraps. And since overpopulation is worst in the poorest areas, (in numbers, if not in terms of resource conumption), capitalism definitely exacerbates the overpopulation problem.
