Worldwide average fertility rate is 2.35, just barely above the replacement rate of 2.1, and it's projected to continue to fall well below 2.1.
Yes, big time
> A natural reduction could be a net good.
Only if it was uniform. Fewer and fewer kids mean within a few generations, we have more and more old people who rely on others to survive. If a society has 50% people over 60 and 50% young'uns, then they have a big problem.