If it is murder, we have an obligation to stop it. (It's against the law)
If it's not then we have an obligation to affirm it. (It's a constitutional right)
So, I will ask again, is it murder? And why or why not?
I don't think abortion is murder. Murder would imply malice, but that doesn't appear to be the case with abortion.
On the other hand, I don't see it as a purely medical procedure either. It's not like having a cyst removed or a tumor.
One way of looking at it might be that, since the fetus is a part of the woman, then a woman who has an abortion might be killing a part of herself. That would make it more akin to suicide than murder. I wouldn't consider it a good thing, but banning it or outlawing it wouldn't really help much.
The main reason we punish murderers is because they're dangerous maniacs who kill people and should be locked up. But does a woman who had an abortion pose a similar danger to society? Probably not.