Nope, not murder - that is a crime defined by the law. The question is, should abortion be defined as murder. I guess that depends on what kind of society we want to have. Do we want to live in a society in which the government, acting on behalf of some group of people, mandate that one individual must necessarily sacrifice their body so that another individual can live?
I don't.
I get all the arguments against abortion, and I admit that some of them are rather compelling. But women - even ones who had sex knowing the potential consequences - still have the right to control how their bodies are used. Saying otherwise is giving government power that I don't want government to have.