You are mistaken here. The LP has never taken the stand you suggest. The official LP position is that a woman's decision to have or not have an abortion is none of the government's business.
This is where most people have a problem with LP philosophy. By sticking to the position that individual liberty always trumps all other considerations, the party has no choice but to take a hands-off approach to an action as abhorrent as abortion. The Republican Party makes room for those who believe that liberty should sometimes be usurped by more important underlying elements.