Those people just don't understand economics. As the abundance of some resource declines its price will go up and the market will come up with some alternative or substitute. Take fresh water for example. As we use more and more of it, it becomes more expensive due to its scarcity. Eventually its price will reach the cost of desalination, which instantly unlocks unlimited fresh water. Another example is garbage recovery. Even as some resources become more scarce, at some point it will be cost effective to dig up garbage pits and mine them for materials. Same thing for oil. Even if we start to run out, which seems unlikely any time soon as we keep finding new oil over and above the predicted rate, alternatives will move into the market. Currently we use oil because it's cheap. As the price goes up due to scarcity we will rely on it less and less. Oil can be made from coal liquefaction, for example, and we will have coal for much longer than oil. Even if coal runs out, we have fission power that can last tens of thousands of years, and this is probably a vast under-estimate as we will find ways to reuse spent nuclear fuel when necessity arises. There's also asteroid mining. We already have the level of technology to engage in it. We just need enough venture capital to fund it. That will unlock a lot of metals that are not abundant in the Earth crust. Another point is that once human-level AI is made, a lot of things will change. It's hard or even impossible to predict the changes since intelligence by its very nature is highly nonlinear. It's silly to try to plan past something that's fundamentally unpredictable. No need to even invoke technologies that we don't currently have or might not ever have, like AI and fusion.