Let's look at a sociological approach to sex. Ignore hollywood's glamorizing and glorification of sex. Let's look at it from a biological point of view. What is the chief goal of sex? Well, that answer is obvious, to some, to procreate. That's not to say sex can't be fun that'd backfire pretty quickly, it is fun and it's intentionally so, it encourages security and commitment between sexual partners. Is sex a right? No. Procreation is a right, more a responsibility for all humanity. If everyone were to stop procreating, what would happen to society tomorrow? Well, there's actually a movie about that, Children of Men with Clive Owen paints a grim picture of a society that is unable to procreate. So, what is the best scenario in which one should engage in sex? Well, this is an easy question for me (religiously). That would be marriage. HOWEVER, this is not about pushing biblical morality or religious teaching. What is the sociologically best situation for sex? Now, this is arguable and I'm (again) not trying to force peoples' social mores to change, but the best situation in which one engages in procreation (which requires sex) is a committed relationship. I'm not going to throw in any extra stipulations or anything like that, but think about social stability. Mother and father both have care over the resultant child. One or both can work while the other can remain with the child to care for it during the child's defenseless developmental periods. Again, this isn't going to apply to every situation; these are generalities that make sense.
Now, since the biological goal of sex is to procreate, what does abortion do to this process? Well, the answer is obvious, it aborts it. Now, wait a second you might say, "What about single mothers?" Does this sociological answer let them off and give them the right to kill the fetus? NO. Not only does this argument work in concert with many other arguments against abortion, one needs to keep in mind what sex is really about. Procreation. The stereotypical love affair in movies, where boy meets girl in X social scene, goes home with the partner, has sex, falls in love or whatever, is NOT real life and that's not a good way to build a relationship. As anyone in a healthy relationship will tell you, if they're honest, relationships need more than one dimension. A relationship only about sex (or any other single-dimensional characteristic) is doomed to fail because some day (usually soon) one or both partners won't have matching sexual desires. Likewise, if it's built on some other single dimension, if that one thing fails the relationship fails, but a relationship built on many pillars is more secure. Don't get me wrong, I don't think the state must get involved in a relationship to validate it. Having that piece of paper from the courthouse really doesn't mean anything. The real meaning is in the commitment made between the two in the relationship (I won't go into the multiple partners area because I find it fairly clear common sense that that kind of relationship is definitely not as secure as one-to-one). Also, the reason a commitment should be public is fairly obvious. Which commitments are more likely to be kept, ones in secret between one or two people, or ones made in front of friends and family? Now, I don't want to go into the social ills of divorce, but it seems obvious (again) that divorce is terrible sociologically. Again, I'm not saying the alternatives don't work. Obviously millions of people grow up without one or the other parent involved; keep in mind we're not looking for a line in the sand, we're just exploring the way things ought to run.
Okay, so this line of reasoning means that every time one has sex one should expect to get pregnant. Right? That's the rational, biological, normal outcome of sex. So why is the question of abortion all about women's rights? I know women's rights have been trampled on in the past, I mean look at how long it took women's suffrage to pass! Women have all the same human rights as men and it's completely moronic to argue otherwise. Women have reproductive rights. Women have health care rights. Women have rights over their own bodies, anyone who argues differently is ignoring the truth of what it means to be human. Those are rights that everyone has and is born with. (Even a biblical argument against women's rights falls apart though many have claimed otherwise.) The fact that the genders are different and fulfill different roles in different situations, has nothing to do with rights, that's one of the strengths of human society. We can adapt and grow better together because we have differences that work better together than separately. That's part of the reason the sociologically best situation for sex and procreation is two happily married (or committed in front of their friends and family) couple. This whole argument for abortion rips at the already feeble fabric of society.
I don't think anyone can stand solely on sociological arguments and say that abortion is morally wrong. Sociology isn't really about making those kind of judgements. Sociology can tell us what works well and the way things really ought to work. Sociology can also seek out variations and show how they can succeed and what types of things will help bad situations work out. But, it's clear that aborting an average of 3,000 fetuses daily is NOT good for society. We need to work together as a society to stop this rift in the way things ought to be.
Based on some comments I'd like to add some edits:
A research paper devoted to studying and comparing the statistics for children growing up in various types of families said this:
Research indicates that, on average, children who grow up in families with both their biological parents in a low-conflict marriage are better off in a number of ways than children who grow up in single-, step- or cohabiting-parent households. Compared to children who are raised by their married parents, children in other family types are more likely to achieve lower levels of education, to become teen parents, and to experience health, behavior, and mental health problems. And children in single- and cohabiting-parent families are more likely to be poor.
This being said, most children not living with married, biological parents grow up without serious problems. In individual situations, marriage may or may not make children better off, depending on whether the marriage is “healthy” and stable. Marriage may also be a proxy for other parental characteristics that are associated with relationship stability and positive child outcomes. The legal basis and public support involved in the institution of marriage helps to create the most likely conditions for the development of factors that children need most to thrive—consistent, stable, loving attention from two parents who cooperate and who have sufficient resources and support from two extended families, two sets of friends, and society. Marriage is not a guarantee of these conditions, however, and these conditions exist in other family circumstances, but they are less likely to.
Emphasis on my points though the conclusion is tempered in the second paragraph with the fact that most don't have serious problems, it's more about individual situations. Again, I don't think this research says that marriage is required to make happy, healthy, productive members of society, but the research is pretty clear on the fact that it does (provided it's a low-conflict marriage). We're seeking what works best, not a solution to all the world's social ills. This is an argument that shows sex/procreation belongs between committed, individuals that are intending to take care of their offspring anything else (especially in excess) is counter-social.