> Why are liberals and conservatives nearly always pro- and anti-abortion respectively?
> how is one's position on the political spectrum supposed to influence something like that?

It's a polarizing issue. The folks that are strongly for/against abortion may start out as single issue voters. Then they start reading the literature and listening to the talk radio that rallies against it. Their soft, malleable minds are then introduced to other kinds political outrage such as church vs. state issues. Pretty soon their worldview has been molded to such a degree that they find themselves agreeing with a party's entire political platform.