I don't think that when people claim that "abortion is murder" they are looking at it in a legal sense. We all have our own interpretations of concepts and of sins; is using somebody else's post-it note when they're not at their desk theft, or not? By definition, it is, because you are taking something that does not belong to you. However, I think most of us would agree that considering it a crime is going a little too far.
Consider. An abortion may not be the termination of what can legally be considered a life, but it is still preventing a life from being lived. If somebody is blowing up a balloon and you decide you'll come along and pierce it with a needle after a few breaths, it doesn't change the fact that if you hadn't come along, a fully inflated balloon would have been the end result. Cause and effect are different, yes, but that doesn't mean they're not inextricably linked.
I'm not staunchly pro-life. I'm in the process of deciding where I stand, with a leaning towards pro-life for the simple reason that no matter what perspective I look at the situation from, I see conception as the beginning of something, and abortion as its end, and that 'something' just happens to be a human life. This doesn't mean that there aren't serious circumstances where abortion could be seen as the 'lesser of two evils' - it's all about weighing up the morality of allowing something to live in pain (to paraphrase the issues involving consideration of abortion) and not allowing something to live at all.
A friend of mine once gave me this dilemma to think about: you come across a wounded animal. It is so badly hurt that you know it's going to die from its injuries, and it is in extreme pain. Personally, I think I would feel incredibly guilty in walking away and leaving it in misery. Does this mean that the abortion of a severely disabled foetus, too, falls under the umbrella of what I would consider to be moral, ethical action? Apply the situation to your own morals and principles.
There can be serious, devastating complications in pregnancies and births. I don't think I'll ever see abortion for these reasons as immoral. It's not as if we are aborting these babies from a desire to do evil works. God knows our hearts, our morals, our strengths, our weaknesses. Our motives. I think we can probably only truly know where our values lie when we ourselves are presented with a situation like that, and will God see it in simple terms such as 'pro-life' and 'pro-choice'? No. God will see how our hearts respond, and therein our true merit with Him lies.
Sorry, that was rather sprawling, but outlining one's views when undecided can be quite tricky.