I think that some form of population control should exist in cases of those who have shown themselves unable or unwilling to support children they create; allowing people living perpetually on welfare with no will or means to support reproduction to continue to be a "baby factory" while being subsidized should be illegal...
...and I speculate the reason it exists is simply a modern incarnation of slavery, and the state and corporations wanting a "steady influx" of new population to serve as future workers.
I'd say for starters, anyone who's had an abortion (other than as a medical necessity) should be banned from reproducing (not sure I'd favor sterilization, but if they produce offspring again they should be arrested and lose custody of their children); though ideally all forms of purely elective abortion should be banned to begin with.
Most likely the solution to prevent people who have no means of supporting children from creating more babies would something akin to a 1-child policy for people who haven't paid taxes within X number of years.
Even though population control is a touchy subject, I think that some type of legislation would have to be enacted as a means of banning abortion as a form of "birth control".