Pro-life, ideally, means that while you dislike abortion and wish that it were not necessary, you recognize and respect a woman's right to choose. It means you fight for education and access to sexual education and birth control.
What happens, though, when those things fail? Because they do fail. Because two people make a child, making it even more difficult for things to be "perfect." I do find that "Abortion shouldn't ever happen so here's other stuff to do" a bit naive, and a bit dangerous. Unwanted pregnancy has always, and will always happen. When it does, are we going to say "Well tough, your birth control failed, stupid you, here's your kid!" We can't do that, and we have to, have to, leave the options for safe and legal abortion open.