A colleague alerted me that Laurie Paul has a piece on deciding whether to have children (in a position where one does not have any yet). Paul addresses the model on which you rationally decide whether to have a child by reflecting on "what it will be like for you to have a child of your very own" and argues that this model cannot be used. The neat idea is that having a child is a transformative experience, and just as the person who has never seen color cannot have any idea what it's like to see red, so too cannot have any idea what it will be like to live after this transformative experience until one has undergone it. Therefore, she concludes, standard decision theory cannot be used to decide whether to have a child.
Now, I agree that one shouldn't decide on whether to have a child by reflecting on what that would be like for you. To decide to have a child on the basis of what it will be like for one is to treat the child's very existence as a means to one's ends. This is morally objectionable in the same way that it is morally objectionable to decide to rescue a drowning person on the basis of what it will be like for one to be a rescuer (though of course that certainly beats deciding not to rescue her).
But Paul's transformative-experience argument seems to me to fail in at least two places. First, it is false that one cannot make rational decisions on the basis of what it will be like for one after one has had a transformative experience. Paul herself gives the example of posttraumatic stress as a transformative experience. I have no idea what it would be like to have undergone that, but I certainly can know that it would be terrible to live with posttraumatic stress. I can decide to avoid situations generating posttraumatic stress in a perfectly rational way on the basis of what it would be like to live with posttraumatic stress--namely, on the basis of the fact that it will be nasty. I don't have to know in what way it would be nasty to know that it would be nasty. There are many very nasty things that are transformative, and one can rationally avoid them simply on the basis of common-sense knowledge (typically based on testimony) of their nastiness.
I think Paul will resist this line of thought on the following grounds. The decision whether to avoid posttraumatic stress or not is a no-brainer given what we know about it. Just about everybody who undergoes it agrees it's very nasty, I assume (I haven't checked opinion polls here). But parenthood is much more complex. Typically, it has both nasty and nice components. And one doesn't know how the nasty and the nice will balance out until one has undergone the transformative experience. But I think that once we've agreed that there is no in-principle difficulty in making decisions on the basis of how things will be after a transformative experience, then it can just be a matter of gathering the best information we have on the balance between the nasty and the nice for people of different sorts, and seeing what sort of a person we are.
Second, even if one could not make a decision on the basis of what-it-would-be-like considerations, decision theory could still be used. One could use non-egocentric decision theory, like utilitarian decision theory. But even within egocentric decision theory, one could make a decision on the basis of non-experiential values, like the objective value of being the intentional cause of the great goods of life and upbringing.
My own take on the reasons for having children is rather different however. There is some discussion here.