You can make many perfectly coherent, secular, based arguments for why abortion is murder. Religion is absolutely unnecessary for this argument. If you take as an axiom that human life is good, and murder is bad, then abortion directly follows as murder. For example, if you would not shoot a baby, as soon as its head pops out of the vagina, but before his body is out. Then you can see that is murder. So what about 2 seconds before that, while the baby was in the womb and in labor?, this is also clearly murder. What about the day before? Day before that? Each of these are clearly murder. There is no clear discrete point, other than insemination where it is not murder vs murder.