On the one hand, you have a life force likely destined to become a human being.
On the other hand, this being is not yet born so therefore does not qualify as a human being (i.e. doesn't breathe air until after birth - a requirement of mammals).
There's a lot of gray area, so here's how I have boiled it down:
To give in to the anti-abortionists who claim it's murder is to basically give them power over your right to have sex. They claim life begins at conception. Therefore, their logic dictates that the actions that take place from the moment a male ejaculates into a fertile vagina should be subject to legislative restrictions (i.e. do not interrupt the creation of the likely being to be born). The logic goes further as it pertains to birth control as well (i.e. abstinence is the only acceptable form of birth control).
Therefore, given the logic of anti-abortionists, I am left with no choice but to say that the woman and man confronted with the issue of pregnancy make their own informed decision based on their own circumstances. After all, would you want others dictating your sexual practices - even if you are married? Does society want to go back to the day of black market abortion doctors with no regard for the woman's well being? Do you think abstinence is the only moral form of birth control and that condoms, pills, and other forms of birth control are the work of the devil?
The choice is clear. Abortions are legal and moral. Sex is legal and moral. Dictating to others how they should lead their own lives is immoral, pompous, unethical and wrong.