*Life* surely begins at conception. But who cares? Cows are alive, and we slaughter and eat them constantly. We end lives constantly, all the time. The question should really be, when can the little thing exhibit self-awareness? Before that point, it's just a clump of unthinking cells. You need a nervous system, and a fair amount of brainpower, to display self-awareness. It's not the 'one thing' that defines us as humans, but it is one of the things that defines a being as sentient. We're not the only species that exhibits self-awareness either -- I believe orcas and dolphins and elephants do as well.
Before it's a sentient being, I don't care what you do with it. After all, it's not sentient, it's got no ability to feel pain, it doesn't think, it doesn't know it even exists. It's basically a tiny Terry Schiavo, but with even less of a nervous system. Her family got to decide her fate, because of her lack of sentience. So too should a woman be able to decide the fate of her own fetusus, since they also lack the sentience to make the decisions for themselves.
The religious harp on about souls. It seems they believe that a sperm cell touching an egg cell spontaneously creates a soul. Any proof of that? What's the soul made of? Where is it located? Can it be frozen and thawed out later? Can you get a soul transplant? How about women who don't believe in these religions? Those religions still have a right to force the woman to term against her will, in effect raping her with their religion? Ummm...no.