I think there are several reasons behind why certain people have cornucopian beliefs.
First of all, they've seen that during the past 150-160 years (since we started using petroleum extensively in 1859) there was amazing technological and scientific progress. That is correct.
We've mapped the human genome. We've sent people onto the Moon. We've created the Internet and computers. We figured out how the brain works. All of these are amazing technological and scientific feats we should be proud of.
However, what many cornucopians don't realize is that virtually all of this scientific and technological progress was due to the usage of petroleum. For example, computer technology only exists because of petroleum since computers are made of plastics, which are derived from petroleum. Virtually all modern technology are petroleum products. And we were only able to make certain ground-breaking scientific discoveries with the aid of petroleum-based technology like computers. For example, we wouldn't have any idea how the brain works if it wasn't for computer-based technology, which is all derivatives of petroleum.
Like Matt Savinar once said, "I don't care if you worship Buddha, Jesus or Allah. What you actually worship is petroleum". He is correct. Pretty much almost every product you are surrounded by was either made or transported due to petroleum. We live in a very special era of human history, which historians in the future might call the Petroleum Age.
Cornucopians argue that we will discover a new energy source that is just as, if not more, potent than petroleum, and we will eventually be exploring other planets on other solar systems many light years away. While it is possible that we might be able to send people to far away star systems, that is not remotely possible within the next couple of hundred years. Also, there is no way we can send large number of people (let's say over 10 million people) to far away star systems because there simply isn't enough resources to build enough space ships. We might be able to send only a few thousand people to a far away star system, but that's it.
What many cornucopians deny is that currently there is no alternative energy source(s) that has anywhere near the potential of replacing fossil fuels. Read the following website to find out why none of the current alternatives to fossil fuels will replace the edifice built by fossil fuels.
http://energyskeptic.com/
And it is likely we will never find an alternative energy source that will replace the edifice built by fossil fuels. I believe that's the case because the world has already been thoroughly explored for alternatives to oil, and none have been found yet.
Even when you exclude fossil fuels from your picture, there are other resources which we are rapidly depleting through over-usage and over-exploitation like various metal ores, rare earth elements (REE), wood, fish, fresh water and top soil. Contrary to cornucopian beliefs, technology cannot solve all of our problems because technology cannot create resources out of thin air. New technology can only use existing resources in new ways, but if you run out of a particular resource, you simply cannot make a certain technology. For example, the people on Easter Island ran out of trees and wood, so they couldn't make anymore canoes for catching porpoises for food.
I believe many people have cornucopian beliefs because they spend too much time watching science fiction shows. Reality is totally different from sci fi! The resource constraints this planet faces will make a high-tech sci-fiction future highly unlikely. Because of the resource constraints and ecological overshoot we are facing, the future will likely look more like the past rather than some sci-fi fantasy world. The future, after the fossil fuel era, might look like what it was during the Middle Ages when most of the energy in the economy was from endosomatic rather than high-quality exosomatic energy. By the way, endosomatic means energy from within your body like the energy used to walk and run. Exosomatic means energy from outside of your body that you can use like the petroleum-used to power cars, trucks, planes and boats.
During the past year of studying peak oil, I have finally realized the ecological niche Homo Sapiens occupies. We were evolved to exploit ever-increasing qualities of exosomatic energy. We started with fire. Then we discovered agriculture, and various tools to amplify the work we can do with our muscles. And then we discovered how to harness fossil fuels for maximizing the amount of work we can do with minimum endosomatic energy. Fossil fuels have been the highest quality exosomatic energy source we've ever discovered, and it is unlikely we will find a higher quality exosomatic energy source than them.
All I'm saying is that current cornucopian beliefs are influenced by watching threads in recent history, and extrapolating them into the future with beliefs based on science fiction. Unfortunately, the future cannot be predicted by extrapolating current threads. Certain realities, like resource constraints and ecological overshoot, make recent threads obsolete in the future. The future will most likely be like what it was during the pre-industrial age where we depended mostly on our own muscle power rather than fossil fuel powered machines!
To end this post, if you want an idea of what the future of farming/agriculture will be like, watch the following video!
https://www.youtube.com/watch?v=dVv597m848s
That's all I have to say for tonight. I hope you enjoyed reading my post.