A human embryo is a microscopic clot of cells and is hardly even visible to the naked eye, much less a fully-developed organism, for many months into a pregnancy.
It's difficult to draw a line in the sand and say "this is when life begins" but I have a hard time agreeing with the notion that something qualifies as a person if it is just a little clump of cells without organs or specialized tissue of any kind, that is entirely dependent on its host for absolutely every function of life there is (except for cellular division).
Obviously, that little clump of cells represents a potential to become a human life, and it may be wrong to prevent that potential from being realized, but it is hardly as cut-and-dried as "this is MURDER."
To answer the question, I think the answer depends on your own personal ethics. Lots of people feel that it is wrong to get an abortion because you just don't feel like having a baby. People have an objection to doing such a serious thing for reasons that are frivolous. Lots of people say "well, you went out and had the fun part of having sex, and now you should have to bear the responsibility that comes with it. It's not right to get an abortion every time you get knocked up because you had a one-night stand."
On the other hand, when someone is raped, a lot of people's objections to abortion end there, because it was not an irresponsible decision by the mother. She had the act forced on her in a traumatizing, violent and demeaning way and it can scar her for life, and it is bad enough that it happened to her - she shouldn't also have to spend the next 20 years trapped into raising a baby she never asked for and that constantly serves as a reminder of her humiliating experience.
Of course, all of this is deeply personal and everyone will have different opinions about it. Also, a lot of people who say that "no, nothing justifies abortion" probably have never been faced with such a difficult decision, and if they were in the same situation, their moral indignation and black-and-white absolutism would probably evaporate pretty quickly.