Hardcore Christians believe that even if you don't believe in God their own version of it must exist, is the supreme ruler of the universe and that other relions and atheism are all flawed, we are sinners going to hell. Unfortunately sinners can produce children as well, in some jurisdictions they can even abort potential children. To Christians children and unborn children are innocent and without choice in the matter, so to follow their faith well they must be good Christians, push their agenda onto others, not allow abortions and attempt to convert children and adults to "the good side", so we can all go to heaven and enjoy pina coladas with a big guy in a fluffy white robe. Abortion goes against what they think to be true so they will oppose it, even going so far as to try and prevent it for people who do not share their beliefs because as I mentioned earlier there is no way they cannot be the ones in the right, even co-existing with pro-abortionists is not possible for extremists because to them we are killing babies and taking human beings away from god, which is Satan's work.