It's a matter of free choice. To this may be added a few points about whether a fetus is a human being, the problem over-population and so forth. But the bottom line is the defense of choice and freedom. Abortion is upheld on the principle of freedom of choice. To deny women the freedom to abort is somehow to seen as putting the axe to freedom itself.
Abortion involves violence and death.
No one denies this. That's the whole point of abortion. We all know this, even the most militant pro-choice activist. We feel a dull ache that we cannot name, we exhibit all the symptoms of someone who has been forced to commit dreadful crimes. And the triumphant cry of freedom is ever louder as a way of masking the real uncertainty, the real shame.