A lot of things would be easier if 90% of people suddenly disappeared, but there is absolutely no sane scenario in which we actively chase such an unbelievably low population count.
The birth rates are declining in large part because of the expenses and time required to raise a kid these days. If life was perfectly easy for anyone to have a child, then the population increases. So, what - you’re going to kill extra children? Forcibly sterilize most? Purposely make life difficult so people lose interest?
This makes no sense at all.
