Earlier quoted context omitted.
Clarify exactly what you mean by "demographic collapse."
https://en.wikipedia.org/wiki/Population_decline
> In the aftermath of World War I, birth rates in the United States and many European countries fell below replacement level. This prompted concern about population decline.[8] The recovery of the birth rate in most Western countries around 1940 that produced the "baby boom", with annual growth rates in the 1.0 – 1.5% range, and which peaked during the period 1962–1968 at 2.1% per year,[13] temporarily dispelled prior concerns about population decline, and the world was once again fearful of overpopulation. After 1968, the global population growth rate started a long decline. The Population Division of the United Nations Department of Economic and Social Affairs (UNDESA) has reported that in the year 2023 it had dropped to about 0.9%,[13] less than half of its peak between 1962 and 1968. Although still growing, the UN predicts that global population will level out around 2084,[81] and some sources predict the start of a decline before then.
In other words, the last time everyone got worked up over this, the trend reversed itself too hard within a few decades, and then reversed itself again. Meanwhile, over half a century after the "decline" started, we have over twice as many people as we had when it started, and the earliest projections for when growth will stop is another half century from now. I think there are a lot bigger problems we'll need to reckon with before then, and if we manage to remain stable by then, it seems like we have good precedent for reversing it fairly quickly.