Even if sacrifice and selflessness were always the same, if one would treat having your own kids differently to adopting a newborn, all other things equal, then

Even if sacrifice and selflessness were always the same, if one would treat having your own kids differently to adopting a newborn, all other things equal, then at least part of your desire to have kids is some kind of "selfish" motivation, rather than a purely altruistic endeavour to bring up a child or contribute to the workforce of tomorrow (or whatever the ostensible motivation is). If one actually only cared about performing a service for the child and/or future society why do the exact genes matter? Unless one actually thinks ones own genes are so superior that they're a service in their own right, in which case, one should be having as many children as possible. Conversely, if one thinks that by having a child is some kind of cost, either to the child or society (or anything other than oneself), it can be a selfless choice to not have the child, even if you personally wanted one.