I've wondered about this. The current world population is close to twice what it was when I started college in the late 1970s.

Comparing what life was like then to life now and thinking about what I'd miss if I had to go back to say a 1976 lifestyle everything I'm coming up with is just that we've now got better technology, more advanced medicine, cleaner energy sources, and we passed laws and regulations to take better care of the environment.

Did we need 4 billion more people to get those things? I don't think so. In an alternate universe where the world decided in 1976 to voluntarily lower the fertility rate to just keep the population at 4 billion I think that 2025 in that world would be a lot like 2025 in our world as far as tech, medicine, energy, and the environment go.