I hardly know where to begin. First, where on God's green earth did we ever get the idea that we should decide whether a human being lives or dies on the basis of whether someone else in society considers the human being WANTED? Wanted is an extremely subjective concept that has nothing to do with whether a person should live or die. Nothing! As you point out, there are many out of the womb children that are unwanted. But nobody (yet) is demanding that it would be more merciful to kill them since they are "unwanted." The day is probably coming, though.
The fact of whether or not the (potential) child is wanted is not the direct reason for the choice. The judgment is made on the basis that it is deemed immoral to bring a child into the world, given the likelihood that that child is going to lead a life of significant suffering and trauma. Is it fair to make the assumption that all conceptions occur when both parties are in a reasonable state of mind to make such a drastic decision? I don't think it is. Is it fair to deny a more informed and rational choice soon after?
Given the number of unfit parents in the world, I think it's a bit strange to force a potential parent to bear a child they willingly claim they're unfit to raise. In fact, wouldn't you think that someone willing to "murder" their own child is likely to be a poor parent, and probably doesn't deserve a child, if we take your standpoint on conception as being the "point of no return"?
That's another point of discussion, where should the line be drawn? Does the fact that I have squandered literally billions of potential humans make me immoral? Should my crusty grey gym sock be viewed in the same light as a mass grave? Is contraception immoral? Are "morning after" contraceptive measures immoral? Is "murdering" a tiny mass of reproductive cells that lack sentience or consciousness any more or less moral than "murdering" abnormal cell growths?
Funnily enough, the backward views various political and religious powers hold are significant factor in unwanted pregnancy. Preaching abstinence instead of sex education doesn't help anyone. It's better to take the logical stance that hormonally charged teens are going to fuck, and it's best to educate them to do so safely, and "morally".* If we actually taught our youth how to act on their sexual impulses in a responsible manner, then unwanted pregnancy rates would reduce significantly, and the abortion argument would be a trivial thing.
Second, what rock have you been hiding under? There are thousands of crisis pregnancy centers set up that specifically give loving support to mothers who choose to let their babies live, including providing housing, medical care, adoptive services, etc. We care about the women involved as much as we the babies--even though it is much easier to wrongly stereotype pro-life people as raving maniacs. Of course there have been a few insane pro-life people. That does not invalidate the work of saving babies from being murdered. Pro-life people also actually care for orphans too. Imagine that.
Okay, I'll admit it's hardly fair of me to seize only upon the stereotypes, but my statement still stands. If the efforts and resources that went toward the rabid opposition of "baby murdering" were instead spent on positive initiatives to care for the children of unfit parents, then once again, abortion would be less of an issue. If a potential parent had the assurances that their child would receive the care and attention it deserved, that defeats one of the "strongest" pro-choice stances.
Surely you'd agree that taking steps to make abortion a non-issue is a more positive tack than bluntly trying to abolish it according to a narrow opinion.
* Unrelated fact, but during Reagan's administration, the US ceased all funding to global aid agencies offering birth control (primarily to Africa). Now, I'm no expert, but last I heard, protected sex was one of the more effective tools mankind has at its disposal to mitigate such things as over-population and the spread of infectious diseases like HIV/AIDS.
** And really, abortion arguments are about the single most pointless arguments to have, due to the divisive stances of arguments. It's like trying to argue which is the one true god. Nobody wins. So there's no need to reply unless you feel like venting. I'm going to bow out having expressed my own views.