I'm a non-libertarian Republican, and I think that the two ideologies have a lot in common, but that does not mean that a Conservative might as well be a Libertarian and vice versa. I support an interventionalist foreign policy when necessary, believe that certain programs are necessary for national security, and think that the government does have a role in enforcing a certain moral code (i.e. not being able to kill unborn children), which puts me at odds with the Libertarian wing of our party.
Republicans who are on the wrong side of things never fail to amuse me with such gems as trying to make abortion out to be murder.
Anyway, it's because Libertarianism is something you grow out of once you're older than 18.
What else is killing a fully developed fetus?