In agricultural societies with relatively small governments the wisest thing for people to do is have lots of kids in order to have relatively cheap labor to help you farm your property, have children to take care of you in your old age, and have a lot of children so that if a few die off at an early age you still have a few left to farm.
In industrial societies with government managed (or mismanaged?) retirement programs children are a net financial drag. This is especially true if the government makes child labor illegal. Also, if childhood diseases have been put in check you don't need to have extra children around to last into your old age.
What people are finding out now, however, is that even with government managed health care and retirement plans, it still helps to have a younger person around to help older people navigate through all the paperwork in order to survive into old age. So I think people will want to try and have at least one child before they slide into dementia.
On the whole I think Feder has it backwards in a way. Birth control and abortion isn't causing people to have fewer children. Rather it is allowing them to have the fewer children they want because they don't need them anymore.
If the sexual revolution came without birth control and abortion then we would be seeing massive increases in population right now. With pretty much every part of the media telling us we have to be having great sex on a daily basis or else we are losers, if there were no birth control or abortion, there would probably be lots of orphanages or lots of people who started out having lots of "great" sex, but are now too tired from working three jobs just to keep all of their progeny fed.