I am not saying that the mother gets to kill a fetus just because it relies on her, but that it is not YET a stage of human life. The fetus is illegal to kill because it WILL provide help to the society, not because it is immoral. I can even argue that it is not immoral to kill a fetus because it has no feelings.
The thing is, the fetus is not a human life, but rather a part of the mother, just like an ear or eye, it is connected to her, though you cannot move your ear freely, just like you cannot move a fetus freely, it is still part of the mother, or you.