A lot of arguments over the abortion issue are tied to religion. I think religions can best be characterized as popularizations of insights gained by exceptional individuals. As popularizations they substitute dogma and ritual for spiritual insight. Thus, I consider religions to be aspects of popular culture that are at best a means of social influence and at worst a method of exploitation. The abortion issue is just the type of emotional issue that religious “leaders” can and historically have used to accrue political and social power to themselves. Up until a few decades ago the hot emotional issue used by many religious “leaders” to garner political and social power was racial segregation. In the future, it will no doubt be something else. I reject any argument marshaled by individuals whose primary motive is probably social manipulation for undisclosed purposes or that rests upon arguments based on religious dogma.
The next line of argument I’d call a “natural law” argument for lack of a better term. This position argues that any living being capable of self-agency owns his or her life (I’d prefer body) and ethically speaking no one has a right to take that life (I’d prefer appropriate that body). The self-agency definition certainly subsumes humans but is not necessarily limited to humans. Thus, the debate comes down to one about property rights, which are defended by libertarians, among others. The sticky point in this argument comes in determining when one has achieved the status of a human being and hence acquired property rights to one’s body.
I do not consider a dividing cell mass a human being. It may have the potential to be a human being but so does a skin flake in your bedding, given the development of cloning technology. Until a developing fetus is capable of sustaining itself outside of a parasitic relationship, it is not a realized human being and has no property rights over its developing body. (Note: Mere birth does not convey the status of human being under the definition used, though there is a high probability that the two will coincide, which in no way implies that one causes the other.) In fact, to give such a cell mass property rights is to put its property rights in direct conflict with the property rights of the host of whose body it is an integral part. As long as the cell mass is in a parasitic relationship with the host’s body, it is for all practical purposes a part of the body over which the host, a realized human being, exercises sole property rights.
The only way to prevent abortion is by the appropriation of a person’s body (property) by threat or physical force. A role usually assumed by the state, but certainly not limited to the state. Usurpation of property rights is not limited to the state and can be done by other types of organizations or even by individuals. Those who wish, for whatever reason, to involve themselves in the property decisions of another have only one acceptable means. They may attempt to affect the decisions of another through rational persuasion, if the person is willing to entertain their arguments. They never have a moral or ethical right to impose by force or coercion their belief or preference on another sovereign individual.