It looks like we can learn from other movements, first and foremost perhaps from the vegetarian movement. Similar to antinatalism the vegetarian movement faces the question of how to make people change decisions that are tightly knit to causing animal (and human) suffering. Similar to parents who like to “have” children, carnivors like to “eat” meat, thus causing the coming into being of ever new myriads of sentient animals.
There might be two major fractions between vegetarians. Members of group A maintain a low profile, they do not try to convince people, they rather try to live on quietly as a still role model. Members of group B, however, act differently: They show around shocking and reproaching pictures from the meat industry that, as a matter of fact, are directly linked to consumer demand. Group B confronts meat eaters with the gruel outcome of their decisions.
One gets the impression that group B is way more successful than group B when it comes to making people change revise their decisions. Therefore, in order to make people change their pronatalist decisions one should make them drastically aware of the consequences by presenting real pictures and by telling real storys. Pictures and stories from illnesses and old age homes for example. But who has what it takes in order to accost pronatal people in such a way?