I don't know if "anti-natalist" can be so simply placed on the conservative vs. progressive axis. Worrying about overpopulation means worrying about the quality of life of future generations, whereas "natalism" à la Musk is basically worrying about how they can keep making themselves richer, while not giving a damn about what happens to the world or humanity afterwards. So Turner's concern about population growth, if not necessarily progressive, strikes me as very fitting and in line with the humanist, philanthropic positions shown by the other points mentioned about him.