Exceptions suggest that the unborn are punishment for irresponsible behavior. If you got pregnant by your own misjudgment, you should be forced to suffer the consequences. If you were forced, and the pregnancy is not your "fault", you should not be forced to carry the child. It's morally confusing to say the least.
Either it is life and worthy of protection, or it is not. The conditions that created it are immaterial. For those that make exceptions, I offer this challenge: at what point would you remove your exception? At birth? A week before? Third trimester? That's the point at which you believe a fetus becomes a child and it doesn't matter how it was created.