The resources of the solar system are infinite, in any sense that matters.
The resources of our planet, however, are not. Do you see a significant number of humans moving off our planet within a couple generations? I admit it's possible, but are you willing to gamble on that?
Oddly enough the resources of the planet have never been greater. Measure available resources per person over history and the graph only points up. Somehow we seem to find what we need when we need it.
Keep in mind that the earth is a closed system - none of the resources are ever lost. You just have to find where they went, and get them again. And the more we need, the better we are at finding them.
The only real input is energy, and that too is infinite. Nuclear power (with reprocessing) can last us for centuries, and I'm sure we'll figure out fusion before that runs out.
I'm an optimist too, but there are a few statistics less pleasant. The average person in developed countries consumes over 10 times what somebody in poorer countries consumes (I won't look up the exact number right now... I remember 30 from the last source but I think 10 is reasonable). I'm talking about resources available with our current technology. We still have to grow crops for calories and forests for wood.
Anyways, if more countries are to reach developed status then no matter how you look at it we have a problem. It's not the apocalypse, but we'll feel it.
Some resources are not very scalable, with our technology at least. Oil is much discussed, but wood is probably less easy to replace. And by far the most important is arable surface. Every food (except fish, which is already not doing so well) depends ultimately on cultivated land. Eating bread and cheese takes a lot less space then eating beef or pork - but the final currency is still surface. And that is not unlimited.
There are other resources too. Every technology consumes some amount of hard-to-replace materials. There are a lot of rare metals in a computer or a monitor. So far the market absorbed any shortages, but imagine a 10x increase and suddenly high prices due to lack of basic materials don't seem impossible.
Even iron is not unlimited. Wikipedia says we have 800 million cars on the roads. Make that 3 billion and you start scraping for steel. Aluminium too. Pretty much everything we mine will see sharp increases in price sooner or later - and it would be very unlikely _not_ to run out of something with a 2x or 3x increase in consumption.
You are assuming we will only use the iron once. But actually iron is reused multiple times, the same can be true for rare metals - especially once energy becomes cheap enough that http://en.wikipedia.org/wiki/Plasma_arc_waste_disposal becomes economical.
What made you think I assume we will use the iron only once? We already reuse it pretty well, that's not the problem. It's simply that 3 billion cars is a lot more then 800 million, and 10 billion computers is a lot more then 1 billion. No matter how well you reuse, you still have greater numbers _at the same time_.
No offence, but at this point I suspect you are not very intellectually honest. I said at the beginning I do not believe this to be a huge problem - solutions will come. But I do not understand your insistence that there is no problem at all.
I don't think you realize just how big the planet is.
And iron is a bad example anyway: the entire planet is made of metal (rock is a metal oxide, usually silicon but plenty of others also).
There are things that we don't have enough of, but if there is a shortage of one element a substitute will be found (for example graphite in pencils, it was available in just one mine which ran out, and a substitute was found).
I did some napkin calculations once. Try it too. Take available land surface (wikipedia or somewhere else) and divide it by population. Then compute the side of the square this surface represents. Take out living space and roads and rivers and lakes and mountains waste land and garbage land and... well, just do the division and you'll see what i mean.
There seems to be limited space, though, not for agriculture, but for actual living. Granted, if we could put all humans into little boxes of 2m^2 and somehow attach life support systems to them and stack those boxes, a lot of them might fit on the planet. Forgive me if I don't consider that a desirable scenario (unless virtual reality makes up for it).
I guess one reason for the success of The Matrix was that it was essentially true ;-)
Edit: to explain, we DO live in a simulated reality, in reality we are stuck in a tiny space with some wires to the outside world. The difference to the Matrix scenario is that we carry the computers doing the simulation around with us (our brains) - or at least so we think.
Hm, thinking again - what about those messages about "fishing grounds becoming depleted" and stuff? Maybe "available resources" can be defined in lots of different ways, and pure energy/person is not the only relevant measurement?
>"Overpopulation" is a phrase used by folks who see humanity as a problem.
We're not talking about overpopulation of the planet; we're talking about a limited geographic area with finite amount of resources. Who cares that Jupiter has valuable hyrdocarbons when your village is starving?
"Overpopulation" is a phrase used by folks who see humanity as a problem.
The more people we have, the more minds we have.
The resources of the solar system are infinite, in any sense that matters.
The more minds we have working on our problems, the better.