Ignoring the idea that an embryo within the stage where it's legal to abort couldn't even be called a lifeform at that point, I fully acknowledge that abortion is murder. An embryo may not technically be a life at the point of its abortion, however, abortion is still stamping out its possibility...its chance at life. The "choice" of life is greedily stolen away from the embryo and snuffed out entirely by its host parent. It will never know the pleasures or pains of life, for better or for worse. And the forcible taking of a life (even if it's just a possibility of life) by another is the very definition of "murder."
You know what's also murder? Masturbation. In fact, masturbation is practically genocide and comparatively far worse than abortion ever could be. The testicles produce approximately two hundred to five hundred million sperm, all of which is released upon ejaculation...all of which subsequently die. Each of those sperm is a potential embryo, each of which is a potential life. Sure, it may not have "fought" through the miracle of chance and became an embryo, but now they'll never have the chance to become one, now will they?
Now, do I see any form of unethical issue with either of these? Not at all. By that logic, then...swallowing would be "cannibalism."
Nathan may have been a bit clumsy in his reasoning (no offense, Nathan), but his point is completely valid. Adoption is not always a good thing. There's a great many children out there that end up in abusive foster families or never find a permanent home. Sometimes this may be preferable to not having a life at all, but not always. And in regards to the accidental parents, they're usually simply not ready to have a child. Their financial status may be nowhere near capable of supporting a child's growth and may ultimately end up destroying their life as well as their child's.
Secondly, as just about any woman who has experienced it can tell you, the process of child birth is a very painful one that not only causes enormous pain, but can also do irreparable damage...or in rare cases, even kill the mother. Does a woman really deserve to bear that burden just because they failed to prevent an unwanted pregnancy?
I honestly don't believe that "They knew the risks" is a reason to negate their choice here. We as Humans beings have a very strong biological urge to reproduce, one that can become downright painful if not satiated in some way, either through intercourse or masturbation. It's a temptation that very few can truly resist indulging at some point, especially in youth where sexual drive is at its highest point. It's really unfair to place blame and force responsibility on individuals trying to fight off that urge when it was not their intention to produce life in the first place.
Lastly, this being my primary standpoint, and one that many of you probably will strongly oppose or even be appalled by, but nonetheless. I fully acknowledge that abortion is murder. However, I really don't care, because it's not the same kind of murder as repeatedly stabbing someone with a knife or other brutal forms of forcibly taking another life. The fact remains that in the stage where an embryo is legal to abort, it really isn't much of a life. Removing it causes it no pain, because it cannot feel pain. It's unfortunate that we're taking its chance at life, but I will always side with the individuals that could potentially have their own lives ruined by prematurely having a child. The life and well-being of a Human that is already on the path of life is more important to me than an unborn embryo that doesn't have a life yet.
That being said, once an embryo develops to the point where it could irrefutably be called a "life", I am mostly against its abortion. But when all is said and done, I am very much a pro-choice individual.