How bad would it be to cause human extinction? ‘'If we do not soon destroy ourselves’, write Carl Sagan and Richard Turco, ‘but instead survive for a typical lifetime of a successful species, there will be humans for another 10 million years or so. Assuming that our lifespan and numbers do not much grow over that period, the cumulative human population—all of us who have ever lived—would then reach the startling total of about a quadrillion (a 1 followed by 15 zeros). So, if nuclear winter could work our extinction, it is something like a million times worse (a quadrillion divided by a billion) than the direct effects of nuclear war--in terms of the number of people who would thereby never live.'
You may agree that that this would be far worse than killing ‘only’ eight billion people and makes it much more important to avoid even the risk of doing so. That’s certainly the view of leading longtermists. But then you’ve probably had the experience of arguing with people who don’t accept this claim at all. Trying to derive it from total utilitarianism—seemingly the most straightforward approach—runs into notorious difficulties. Many philosophers deny it. Instead, like many laypeople, they accept what John Broome calls the ‘intuition of neutrality’: ‘for a wide range of levels of lifetime wellbeing, between a bad life and a very good life, we intuitively think that adding a person at that level is neutral.'
Broome thinks the intuition of neutrality must be wrong, and offers some proofs. I think there’s a simpler reason to doubt it. (N.B.: I'll bracket the effects of our survival on non-humans.) Suppose a government is considering developing vaccines against two strains of flu. If the first mutates and crosses into the human population, it will kill seven billion people immediately. After that, most people will develop immunity, but it will still kill ten million people a year for the next thousand years. If the second virus mutates and crosses into the human population, it will kill everybody on earth. Each virus is estimated to have a 1/1000 chance of mutating.
Most of us will agree—I hope—that the government shouldn’t discount the ten billion future deaths that the first virus would cause just because they would arrive in the future. It should count the expected deaths from an outbreak as 17 million (1/1000 x 17 billion). In contrast, the expected deaths if the second virus breaks out are only 8 million (1/1000 x 8 billion). If additional human lives have no value in themselves, that implies that the government would have more reason to take precautionary measures against a virus that would kill most of us than one that would kill all of us, even if the probabilities were equal. If it could only afford to develop vaccines against one of them, it should choose the first.
That seems to me a reductio. Do you agree? Or am I missing something?
Postscript: Judging by the first two comments on this post, I must have failed to make myself clear. I believe the second scenario is at least as bad as the first, and that this undermines the ‘intuition of neutrality’. See my reply below.
Still, I think your argument is in fact an argument for antinatalism, or can be turned into one, based on the features of the problem to which you've been sensitive here so far. If you rejected antinatalism, then your argument proves too much and you should discount it, or you should be more sympathetic to antinatalism (or both).
You say B prevents more deaths, because it will prevent deaths of future people from the virus. But it prevents those future deaths by also preventing those people from existing.
So, for B to be better than A, you're saying it's worse for extra people to exist than not exist, and the reason it's worse is that they will die. Or that the will die early, but early relative to what? There’s no counterfactual in which they live longer, the way you've set the problem up. They die early relative to other people around them or perhaps without achieving major life goals they would have achieved if they didn't die early, I guess.
Similarly, going extinct now prevents more deaths from all causes, including age-related ones, but also everything that causes people to die early, like car accidents, war, diseases in young people, etc.. The effects are essentially the same.
What's special about the virus in this hypothetical vs all other causes of (early) death in humans?
So, we should prevent (early) deaths by going extinct now, or collectively refusing to have children, if the alternative is the status quo with many (early) deaths for a long time. That looks like an principle antinatalist position.