Being human is sinful, living is sinful, breathing is sinful. The only thing that isn't sinful is doing and believing everything your religious leaders tell you. Actually, you'll probably screw that up too.
Non-Believer: What about original sin? The fetus is rotten with the taint of Adam and Eve's disobedience. Hell, that fetus doesn't even believe in Jesus.
Believer: The child must live so we can indoctrinate it into a confused cycle of self-loathing and smug righteousness.
It is the goal of every human being to learn what is right, become a moral agent and save himself through virtuous action.