The great thing about "markets" is they are self-correcting.

Suppose I could make tremendous profits selling hand-held personal nuclear weapons to everybody. I sell a few million, the world gets vaporized and along with it my money and my life. Realizing this is the likely outcome, I don't sell those weapons. More profitable not to.

Of course it doesn't work perfectly, but like "overpopulation" -- if we use up all the oil and can't figure out how to replace it, or pollute the earth to the point where life expectancy falls and we can't grow enough food, etc. -- Mama will kick our asses and we'll be right back to the stone age or extinct.

To the extent we can anticipate these problems (obviously we can, we're doing it right now) we can take steps to avoid them.

I've never said "buy an SUV and drive everywhere, oil will last forever" have I? I am a strong advocate of developing alternative energy systems. The difference is I am confident we'll be able to before the crisis point -- hence the crisis can be avoided.

It really boils down to optimism vs. pessimism I suppose.