Just so you know we're fair and balanced, Eric Pianka believes that the probability of an emergent infectious disease (or perhaps more than one) causing a human population crash is substantial:
Some politicians, economists, and corporations want us to believe that technology will come to our rescue. But we have a false sense of security if we think that science can respond quickly enough to minimize threats from emerging diseases. Microbes have such short lifecycles that they can evolve exceedingly fast, much faster than we can respond to them. Many bacteria have evolved resistance to most antibiotics, and viruses are resistant to just about anything. Defense always lags behind offense. So far, modern humans have just been lucky. A reactive approach to problems isn't enough, we also need to be proactive and anticipate problems before they become too severe to keep them from getting out of control.
I'm still skeptical about that, but he does make the point that since the globe is far more crowded with human beings today than ever before, and since travel around the globe is possible in a few hours, a plague would not be limited to a single continent, as the Black Death was to Europe or the demographic disaster caused by smallpox was to the Americas. I will just reiterate what I have said here many times: we need to take the problem of antibiotic resistance very seriously, and we need to develop new vaccine manufacturing facilities based on cell culture techniques that can ramp up manufacturing of novel vaccines quickly and in large quantities.
And then, yes, we need to work to reduce the human population over time, by making contraception universally available and raising the status of women. We need to do whatever we can to reduce the use of fossil fuels, since global warming increases the dangers from infectious diseases. We need to build strong public health infrastructure around the world. We need to provide everyone with clean water. We need to change our methods of animal husbandry (and eat less meat while we're at it.) Whether an emerging infection kills 1%, or 10%, or 90% of the population, it won't be pleasant. Pianka isn't exactly wishing for it, as he has been unjustly accused. But he seems to see that 90% event as inevitable. Let's make sure he's wrong.