Why "choice" is a bad argument
First, I think women should be able to choose to have an abortion.
The problem is when pro "choice" activists use that as an argument in and of itself. It is a TERRIBLE argument for abortion as it bypasses the main issue entirely.
It's not complicated. Pro life advocates consider a fetus more than a mere cluster of cells, they consider it a human being with the same or nearly the same moral weight as their spouse or sibling or older, born, children.
For pro lifers, if you genuinely held that a fetus had THAT much weight, then the "choice" argument makes no more sense than applying it to a 2 year old child. To the person who considers a fetus as virtually indistinguishable from a grown person, choice is a meaningless word, you do not get to choose whether or not your 5 year old lives.
This is why choice is such a terrible argument. The more basic disagreement is over the nature of the fetus itself. I hold that a fetus is well below the threshold of personhood, as such, I tolerate abortions as I do NOT see it as the same as killing a 10 year old.
But make no mistake, if I DID see a fetus as having the same as an adult or born child, then I too would be against abortion.
A better tact is to argue over why you think pro lifers conception of a fetus is flawed, not just to you, but even to themselves if they thought it through.
Of course, peeling away layer after layer will often lead to a more basic foundation, a religious belief that a soul enters the fetus at conception. That is a foundation that cannot be argued away without undermining a whole set of their religious beliefs as well. And certainly not by arguing for some basic right of choice. You may as well speak to the person in another language for all the bearing that has on the more basic difference in beliefs, the nature of the fetus.