The thing is I don't think they do. If they really believed that a single fertilized ovum was equivalent to a child and that millions were being murdered by birth control, they'd be bombing CVSes. Saying a single cell is the moral equivalent of an adult human is lunacy on such a level I honestly can't even understand it.
But more importantly, even people actually fully opposed to things like birth control (which prevents an already fertilized ovum from implanting into the placenta) don't treat it as if it's actual murder.
Once you have something that could be born and survive just fine, it's hard to say at that point you have something that is either fully a human life or so close to it as to be deserving of moral consideration.
Even at that point, though, there are things like a placental abruption. Basically the placenta fails massively and it's an immediate medical emergency. Usually they can save both the mother and infant. Sometimes, though, the only choice is to pick one, and that's going to be the mother. Under the laws currently being proposed, whoever saved her life would be subject to criminal prosecution so they'd have to just sit and watch her die while doing nothing of use.
It used to be the majority opinion, of the public and even the Supreme Court, that this was okay, and Justice Oliver Wendell Holmes, Jr., one of the most well regarded of jurists to this day, specifically. As he famously stated in Buck v. Bell, upholding the sterilization of a retard (although today there is actually some question as to the veracity of the actual diagnosis): "Three generations of imbeciles are enough."
You can really blame Hitler for giving the whole thing a bad name. Too bad because there are definitely people who shouldn't be fucking reproducing. I guess I'll just have to cope, because I suppose having these goddamn retards around is better than having the kind of tyrannical government you'd need to do anything about them.
