If the reason for going against abortion is to protect human life, then allowing it in cases of rape or incest make no sense at all and break that logic. The only logical reason to allow a rape/incest clause is if your REAL reasons are that you think people should be punished for their mistakes more. So, no, that doesn't really work either.
Abortion is an unsolvable issue because the yay and nay of it relate to philosophical concepts that have no factual answer. Fetuses/zygotes/embryos/sperm cells/egg cells are all "human life," so none of that is in question. The question is "personhood," which is a philosophical concept, as it relates to when someone else's personhood overrides the mother that it is feeding off of's wishes. And there's no "true" answer to that because everyone doesn't agree on when that starts.
The U.S. Supreme Court set it at viability - when it can reasonably survive outside of the mother, which also happens to coincide with where it actually begins to think and feel. That's a logical stance based on the available actual data that we have.
Really, the biggest issue is so many people being raised in a human-centric religious atmosphere in which they are force-fed the idea that human life is the most important thing ever and must be preserved at all costs, no matter what because it's ultra special because it is. That causes people to think of even something as non developed as zygotes, which think and feel less than worms, as more precious than the self aware, fully feeling dinner they had that night, and assign it more importance than they actually do fully grown people who actually -do- suffer and die constantly around the world.