@Isaac, I agree that there is a slippery slope here.
Forget drugs, just insert anything. Point is the same
Not entirely true. Abortion differs from drugs, alcohol, tobacco, gambling, ... pick your other poison - in one significant difference.
The problem with abortion that differs from other human activities is one of agreement on what just happened at a philosophical level during that abortion. I also have to say that I'm playing Devil's Advocate on this because my wife and I agreed that if a child was born to us we would keep it. So my answer is not based on what I would do if WE had a pregnancy, but what women IN GENERAL face with a pregnancy.
Various religions differ in the beginnings of being a person. Judaism says it is when the umbilicus is cut. Some evangelical denominations use the Solomonic definition, "The breath is the life" (referring to "first independent breath.") Scientifically, defining the start of "personhood" requires a scientific test for being a person, and I have known some folks who were upright and walking that might not make it within such definition. Not to forget that some parents, due to beliefs in certain fundamentalist religions, have the right to withhold medical treatment from their child (putting said child's life in God's hands) - which historically has resulted in death of the child AFTER it was born.
This means that there is no
universally accepted definition of the discrete and unequivocal beginnings of a person's life. Therefore, at least under the US Constitution, there are two relevant issues. First, the USC says that rights accrue to persons BORN or naturalized to become citizens. Legally, birth is a critical condition. Second, the multitude of personal creeds is protected because discrimination is not allowed based on personal creed. If a person's creed or religion says that the fetus (clearly not born yet) is not a person, then what is abortion? It is not murder if there was no person.
We can all agree (I think) that a person who is walking around, talking, chewing gum (not necessarily all at the same time) and doing other person-like things should not be shot and killed. Or stabbed and killed. Or whatever other method floats your boat. That killing qualifies as murder. But the way laws are written in some states, a cluster of cells the size of my thumb, something that might not yet have developed a brain stem, is still a person and abortion is murder. I'm sorry, but at that point you are on very shaky philosophical ground to say that.
Part of the problem is that lack of a universally accepted definition and the fact that individual beliefs are protected in this country. Therein lies the crux of the discussion. It is not what I believe; not what you believe; but what the aggregate of people believe - and that aggregate does not include a consensus on the start of personhood.