I don't think you can completely discount radical Malthusianism. While such a scenario is unlikely at this point, it isn't impossible. If we were to head into the final fossil fuel depletion tail spin with no real alternatives, it would happen... but it's starting to look like we do have alternatives.
The question is will it happen everywhere or be localized, I doubt that it could happen world-wide, but in some parts it could happen it happened before and could happen again.
Anyway a lot of scientist become extremist and can become scary. If history can tell something is that even the besto of scientists are bad prophets.