Abortion has been so villified in the past because, like birth control, it further separated sex from reproduction. For some people (and for a variety of reasons), this is a very negative evolution of our humanity and of our understanding of ourselves and of our bodies because it alters and changes what some believe to be a "natural" function.
And, when sex was separated from reproduction, women became more free to experience and express their sexuality in ways that gave them pleasure. Many more people see this as a negative development either because it led women to be more like men in their relationships or because it led women to be more free in other areas of their lives. If you can control your fertility and absolutely make it align with your personal will, you can do anything else you choose to do. This means that more women have decided to put off childbearing to go to college, develop their own satisfying careers, and to even forgo marriage. To many people (obviously not me) this was a very negative development that led to the further changing of our basic family structure and to women's rights and responsibilities in general.
Those are all nonreligious arguments that I have heard but I have tried to express them in a more rational way than they were expressed to me because the argument that abortion and birth control should be illegal so that women go back to their antiquated gender roles whether they want to or not does not hold any weight or validity with me. But I have had enough sociology to understand why people fear the vast changes that have occured and may even try to fight against them.