Models or goals that require continuous growth tend to be unsustainable. Looking at nature, most living organisms have a finite mature form.
Systems like GDP are great in a stage of economic growth, but once a mature economy has developed GDP no longer indicates economic improvement.
Similarly, population growth is useful for expansion, but in my opinion not necessarily a valuable goal in the world right now. Although some might be wary of the consequences of population stagnancy or decline, there are actions that can be taken if those in leadership foresee and accept these situations. Some of the most prominent modern population realities and consequences are described in detail by polling expert Dr. Darrel Bricker in The Inquiring Mind Podcast ep. 40.