That's only partially true. There is a massive ... excuse the term ... market for newborns when it comes to adoption. The "unwanted children" tend to be the older kids who are passed over because parents tend to want infants rather than older children with existing problems. Another infant put up for adoption does not necessarily displace anyone.
What I found in my brief search was that unwanted black babies are plentiful in the U.S., but white babies tend to be adopted from Europe and sovblock states. Maybe there are too many of both, and families just prefer foreign-born infants to U.S.-born infants. Maybe I was wrong about the global adoption situation, but I'm not sure the situation is as simple as you describe, either. If people are selecting infants based on race, maybe the abortion/no-abortion policy decision would best be made on a per-race basis? And because of the ethical problems I can already envision with that proposal, and the fact that the world population is growing unacceptably, doesn't it make sense to minimize the number of delivered babies? Nobody has a right to adoption, even if there is more demand than supply.
I'm sure that there are some pro-lifers out there who use that definition but it is not mine.
Tell me, tyme, what defines a person to you? Under what conditions should a squirming mass of cells be given human rights?
You realize, I hope, that most animals are "squirming" masses of cells at some point? You can't seriously want to give human rights to them all? It seems to me that you want some magical nexus between "squirming" and human DNA to magically confer protected legal status as a human being. Human DNA doesn't make anything special. Given enough money, humans can now construct arbitrary DNA sequences. Constructing something as long as a human chromosome is probably still virtually impossible, but I doubt it will remain impossible for long. And what about hybrids... humans with some genes removed and some other genes inserted? Are they genetically human? Where do you draw the line?
These following conditions are rough, so please consider the intent as well as the literal meaning. I think it's reasonable to grant infants legal status as humans when:
They exhibit the capacity for problem-solving at a level above that of other primates.
They exhibit the capacity for communication and social-interaction. (This is severely problematic because some primates exhibit this as well, but this is artificially "fixed" by the other two criteria.)
They must be genetically human. Whether this means people with severe genetic mutations, but with human parents, are not humans is open to interpretation. Or this could be re-written as "must have human parents," although then we have the problem of whether a human-equivalent evolved from some other species gets any legal rights.
Those criteria let infants become legal persons by their own merit at roughly age 2-3.
Legal status as human starting at birth is problematic. I wrote a longer screed about it earlier, but decided I didn't want to get involved in such a divisive discussion. But you asked, so...
Parents (and infants) exhibit biochemically-induced psychological bonding with their children (and parents) in a short time after birth. Legal protection for newborns is therefore justified to reduce 3rd-party harm to newborns, which has serious emotional and psychological consequences for the parents. There's also the social problem that parents tend to have an overwhelming urge to seek their own extra-legal justice when something happens to their children. By discouraging harm to infants who do not yet merit human rights on their own, the law can reduce instances of parental extra-legal justice for harms done to those infants.
Even relatives, neighbors, and friends bond with newborns of families in their social circles. They also have an interest in reducing harm to others' newborns, to prevent their own physiological distress.
I think the line should be drawn at whenever a child advances mentally past the abilities of primates. That idea that 3rd party harm is enough to justify prohibiting murder is very sketchy, and I'm sure it has some problems. Nevertheless, I think the core idea is solid. It's easier for everyone to draw the line at birth because everyone, myself included, feels instinctual revulsion at the idea of killing a breathing, crying human baby, even if it's 1 day old. So it makes sense that laws against murder, beginning at birth, are more to give us an outlet to do something about our revulsion over the killing, rather than to punish someone on behalf of a self-aware individual who can no longer seek revenge on his own.
You can't instill responsibility into would-be parents by making it illegal to abort the product of their irresponsibility.
Can you instill responsibility into parents by making it illegal to kill their toddlers? No? Then why is it illegal?
Because they should have aborted the toddler earlier. The line has to be drawn somewhere, and there are reasons (outlined above) for drawing that line at birth.
You're completely missing the point. The couple who had sex are the ones who want to burden everyone else with the social and economic consequences of their actions. I personally am simply against the killing of their would-be child.
What consequences are those? There are only the moral and psychological consequences for those who decide to take upon themselves everyone else's problems, and as a result are traumatized when some other family decides to have an abortion.