According to science, the only thing that can change the second derivative of population is public policy? What has caused changes in this number throughout history?
The debate would go much nicer if you could just explain your point of view, which I kindly asked you twice now. Instead you are asking me what I assume are rhetorical questions from your perspective.
My point of view is that it is not useful at all to carry out predictions assuming that the second derivative of population will stay constant for a long time and that it is even sillier to propose public policy based on this.
By that logic we should not act upon anything. E.g. if a car is accelerating towards you while you are crossing the road it would be prudent to speed up or delay your crossing and not to ignore it and say they will surely decelerate at any moment now.
