If you want to shrink a population, you have to do it slowly while adapting the system to it. In a few years, with the boomer generation slowly retiring, Europe would be fucked without immigration. Too many retired people with not enough young people to care for them and uphold the economy at the same time. You can't fix the resulting hole in manpower by only increasing efficiency. In Germany we are talking about a lack of 400k people per year.
Nah. We waste human resources on things that could be done automatically, look at our entire Government, all the wasted resources because some old ass bastards in politics aren't able to commit to the new world.
We could also just optimize efficiency and not make more people.
Less people means more wealth, as wealth is a limited resource on earth we need to share it, if we reduce the shares we all have more. There is absolutely no need for more when less gets the job done as well.