"full body autonomy" includes but is not limited to "no one [is] forced to let anyone else use their uterus". I don't believe I am sabotaging my own argument, but I'm an idiot, so maybe you just need to be more meticulous in explaining how I am (doing that).
I bring it up because authoritarians often try to restrict bodily autonomy, particularly around uteruses, when trying to do population control (up or down). In fact, while it may not be a acceptable, mainstream view, you don't have to look to hard to find a USian on the right claiming that abortion must (become/stay) illegal because of the "birth rate crisis".
Agreed. I think globally we are still above replacement rate.
Yes, but no. As the video I linked points out, because of the time delay you get fewer people with maximum productivity while still needed to support people that have sub-self-sustaining productivity. Eventually, you might get to a smaller population that choose to return to above replacement rate, but the demographic squeeze don't got away for another 20-30 years. Once it starts you are stuck in a demographic squeeze, it makes it even harder on everyone, making that choice "harder".
That is a simplification. Sub-self-sustaining productivity doesn't exactly track with age, and how much it takes to sustain a joyful life varies based on a lot of factors; it sort of tracks downward but can also go up if economies of scale shirk or when a new essential utility is introduced by technology.