The fact of the matter is that most of the time, folks already exercised their power of choice when they engaged in behavior that results in babies.
That's true. However, it misses one big point. There is one religious denomination that neither believes in birth control or, basically, in methods to prevent contraception. They don't teach about birth control in any of their many thousands of parochial schools, either.
For religious denominations that provide adults with sex education unwanted pregnancies are very low.
Abortions result from unwanted pregnancies. Among Jews, unwanted pregnancies are so low that the abortion rate is also very low. The same is true for many of the Protestant denominations that provide age-appropriate sex education.
However, abortion remains a big problem for just one denomination that keeps its members in the dark when it comes to sex education, methods to avoid contraception, etc.