The repugnant conclusion.

This paradox in ethics is called the repugnant conclusion. Many people would agree with the following when it comes to designing a policy that affects people's quality of life and the size of the population.

1. A world with 10bln people and high happiness for each is better than a world with a gazillion people whose lives are barely worth living.
2. A world with x people at some happiness level is not better than a world with x people at the same happiness level, plus additional y people who are happy enough to make their lives worth living (original people are just as happy + new people would rather exist than not).
3. A world with one group of people at a higher happiness level than another group is worse than a world with everybody at the same level and a slightly higher aggregate happiness (more equality + more overall happiness).

But this leads to a paradox. Suppose 0 indicates the level of happiness that's on the threshold of being worth living. Start with 10bln people at happiness 100 each. By 2, we can improve the world by adding another 10bln people at happiness 50 each. By 3, we can improve it further by redistributing the happiness equaly, 75 a piece, and then making it slightly higher, say 76 a piece. Overall, we have twice as many people now, at roughly 3/4 of the original happiness level.

We can perform these two steps again and again, each time doubling the population but decreasing the happiness per person. At each step the world improves, or at least doesn't get worse. After many iterations we will arrive at a world with a gazillion people whose happiness is barely above zero, thus contradicting 1.

I will post my solution in a separate article. Meanwhile, let me know in the comments how you would get out of this conundrum.