I'm always unconvinced by Malthusians, especially when those predictions involve the exhausting of arable land. That prediction has come and gone since before Malthus became famous for making it. The actual carrying capacity of the Earth is unknown, though obviously (1) it certainly isn't infinite, and (2) every time we expand we make less room for other species.

I certainly wouldn't be surprised if by mid century almost all species of large mammals were endangered or extinct, but that's a far stretch from societal collapse. Of course, the more we talk about this stuff, the less people are excited to breed, and the shrinking of the populations of the Western world have to be considered when trying to make bets on the future. What if the birth rates in poor countries start to approach those in rich countries? This isn't a remote possibility, and surely that would forestall a lot of the most dire predictions.

I think it's a valuable exercise to think about worst-case scenarios, but I think the risk is in putting too high of odds on worst-case as an inevitable outcome.