I am not a doomer, nor a Malthusian, merely a realist. There are a few points I could make briefly:

- Everything lasts forever, until it doesn't. Ancient Egyptian civilization lasted for thousands of years, until it didn't. Any Egyptian could point to thousands of years of their heritage and say it hasn't ended yet, therefore any prediction that it will end is clearly bad and dumb. Then it was conquered by Romans, and then by Islam, with its language, culture, and religion extinguished, extant only in monuments, artifacts and history books.

- We have nuclear weapons now. Any prediction of an imminent end of human civilization before then would be purely religious, but there is a real reason to believe things have changed. We are currently in a time of relative peace secured by burning resources for prosperity, but what happens when those resources run out and world conflict for increasingly scarce resources is renewed with greater vigor?

- Note that I did not outright predict the end of human civilization, merely noted it as a plausible worst-case scenario. If civilization continues on more-or-less as it is, in the next couple of hundred years, we will drive countless more species to extinction. We will destroy so much more of our environment with climate change, deforestation, strip mining, overfishing, pollution, etc. We will deplete water reservoirs and we will deplete oil, helium, phosphorus, copper, zinc, and various rare earth elements. Not a complete depletion, but they will become so scarce as to not be widely available or wasted for the general population's benefit. If billions of people are still alive then, which I explicitly suggested was a possibility, they will as a simple matter-of-fact live much less comfortably prosperous lives than us. It will not take a great catastrophe to result in a massive reduction in living standards, because our current living standards are inherently unsustainable.