Not GP but I do say the same, and yes it will be uglier than the first half of the 20th century. The fight for food will be very real and it takes away confidence from my family planning.
If every woman gives birth to less than ~2.1 children, we're shrinking. Is having <= 2 children painful and ugly?
Humans live for decades. Catastrophic climate change is less than a generation away. It would take hundreds of years for the population to shrink enough to stop it.
That's not how "natural self-regulation" works. People aren't PID regulators and don't suddenly adjust their fertility to not exceed the carrying capacity of the environment.
Natural self-regulation means hitting resource limits, followed by sudden and drastic mass dying off, through wars and starvation.
This so called natural self-regulation will be ugly and painful. I don't envy the generation that will have to go through it.