Why do you have to incentivise an increase in the birth rate? Why does it always seem when there is a discussion of birthrate, it's somehow automatically assume

Why do you have to incentivise an increase in the birth rate? Why does it always seem when there is a discussion of birthrate, it's somehow automatically assumed that low-birthrate == "bad", with the obvious next point being that it has to be fixed. Honestly, from my point of view as a free-minded individual, this is exactly the sort of thing that is quite frankly disturbing about government intervention. Society is seen as some sort of grand-experiment that needs to be tweaked and prodded in order to optimize X or reduce the risk of Y, in endless different contexts.