Abortion is, and will always be a difficult theme, and there aren't any right answers.
First of all - the age of the fetus/baby does matter. Until the fetus is around 23 weeks, it is usually not viable outside of the uterus no matter how many medical resources you put in to save it. Nowadays, most babies born after 26-27 weeks survive, even if they often need medical attention for a while, and some develop long-term medical problems. Babies born after 32-33 weeks can usually manage fairly well without a lot of medical care, as long as they're taken good care of. Basically, a baby that can survive outside of the womb should be given the chance to live.
However, until the baby is viable outside the uterus, it is a part of the mother, and is basically a part of an organ. Essentially, a fetus is also a kind of "parasite", borrowing the mother's resources and making the brain do crazy things so the host's body won't reject it (also known as hormones). If any other parasite was inhabiting a host body, and was causing harm to it, the parasite would have to be removed. Most fetuses that aren't viable or are rejected by the mother's body for other reasons will spontaneously abort anyway. If the fetus is causing harm to the mother's body, abortion should always be allowed - to save one life, instead of killing two lives. If the baby can be saved by taking it out, then all the better.
One might argue that a fetus has feelings and all that, but a fetus is basically just a lump of fast-growing cells for the first 6-7 weeks, and doesn't actually sense or even do a whole lot until the 2nd trimester starts, and for a while it's just going through basic testing of body functions that the fetus won't remember for long, if they even remember things at all. We don't treat other fast-growing lumps of cells the same way, even if those cells are alive too (normally they're removed, and treated as something bad).
Then there's the social aspect. Should unwanted babies be pushed on someone no matter what, when and how? Unwanted pregnancies can turn up when least expected, even if using protection, and not everyone can handle it. Perhaps they want to wait, or maybe a child just isn't in their plans, since not everyone wants kids. Some people shouldn't even be allowed to become parents - and those tend to be on the forefront of people who got kids at a very bad timing in their life, or shouldn't even be around tiny humans, let alone being allowed to care for them.
Then there's things like genetic diseases or syndromes that are discovered early in the pregnancy. Some people might choose to carry the baby to term, and will love and care for the child no matter what's wrong - but not everyone have the resources, economy or time to take care of a bundle of mostly worries. Knowing you have to take care of a cronically ill child can be a very big burden - and not everyone is up to it. Sure, some children get sick later in life, but then you've gotten to know them, held them in your arms, and had those moments of absolute joy, and then you'll be willing to do everything in your power to help them. There is a distinction between the fetus being still inside the womb, and actually seeing, feeling and touching the little bundle. That's probably also why people usually don't go killing off their already born kids.
I feel the distinction should be on when abortion should be allowed, not the if. Where I live, it's selective up to 12 weeks. After that, abortion gradually goes from being a relatively small procedure versus being an actual birth. From 12 to 22 weeks or so you have to apply to do it. After that, it's probably the mother's/baby's health that decides. Basically, it depends on where the baby goes from being completely dependent on the mother, to being viable outside the womb with medical care. One aspect has to do with ethics - in one room you know you're ending the life of a 21-weeker, and in the next you're doing everything you can to save a 23-weeker. It is hard on healthcare personnel, and most likely even harder for the mother if it involves an actual birthing process - particularly the time after.
Basically, up to 12 weeks I think it should be the woman's choice, but I am against it being used for the wrong reasons, such as wanting one gender and aborting if it's the other. I'm not for the use of "morning after" pills or an abortion procedure as a protection method because someone is too lazy to use proper protection while they're having fun. After 12 weeks, abortion should be legal but regulated, and it should be a fast-track process, because fetuses don't tend to wait around for people to decide one way or another. I also think there should be some kind of councelling session, because in some countries you can get a lot of support during and after the pregnancy, and people might not even know the option exists, and some women may be in a situation where they want the baby but for some reason can't have it. Basically an option to know you can regret the abortion before actually doing it. A lot of women suffer from regret and even depression after abortions, and hving someone to talk to who isn't biassed either way can be a big help in taking the right decisions.
I won't even go into the discussion of religion VS abortion, because mixing religion with medical questions (particularly abortion) usually tend to be a bad thing. I'll say a couple of things, though. Babies aren't miracles, because babies happen every day. Miracles don't. It's kind of in the word. Babies happen because two cells blend DNA together and go on doing what cells do best, because they're programmed to do so - divide and grow. In addition, a lot of potential babymaking cells are lost every day without anyone caring much, and if all of those had been allowed to develop, we'd overcrowded Earth a long time ago. Besides, having someone telling you what to do with your own body, based on a book from a time where childbirth was one of the riskiest tings a woman could do, might not be the best option.
There's also the tough question of whether or not a woman should be forced to keep a baby after being raped. I'm a firm believer in that it should be the woman's choice. Of course it's not the baby's fault who the father is - but the baby will for some be a reminder of what they went through. Some women aren't able to see past the hate for the rapist, while other women would love the baby regardless of how it came into being.
When abortion is illegal, it leads to a whole lot more deaths, because women often get desperate and end up doing stupid things that does a lot more harm to their bodies than a properly done abortion.
I don't know what I personally would have done in a situation where abortion might be an option, but I do see the for and against opinions, and vote for it being legal but somewhat restricted, and against it being illegal.
(Just so it's said - I love babies, and therefore I'm not for abortion being used where it shouldn't. If you don't want a baby, use protection, and double it up if you can, with both partners using protection. It's safest, and protects against other things than just unwanted pregnancies. Abortion should be considered a last resort, but making it illegal doesn't gain anyone).