Abortions shouldn't be necessary in a modern society (medical complications aside), birth control is effectively free, all it shows is a lack of responsibility from all parties involved. I think over a million abortions are performed a year in the US? An absolute tiny proportion of those would be from incest/rape. There is definitely a moral arguement to be had against the procedure being used, you are essentially killing a life, unless you're prepared to define what stage in a babys development it isnt a life.
The rape/incest angle is always argued in cases of abortion, it's a fallacy to use this absolute minority of cases and apply it all abortions performed.
There is a case for both sides of this and it's a complicated issue, with how easy this is to avoid via birth control its ultimately a failure on the part of the parents.