Abortion wasn't a huge issue until the 70s, when some religious conservatives took it upon themselves to start a revolution. They twisted and lied about what the bible said. The bible is actually pro-choice and this was the majority of the conservatives viewpoint as well until it became a nasty thing the lefties do. It never specifically mentions abortion but does mention what is considered beginnings of life and also that sometimes a child may be better off not being born. Most of the verses from the bible that Christians use to support a pro-life argument are actually part of a larger story and they (conveniently) leave out the bit that shows it was a specific example and not for people on the whole.
But regardless of all that, it really comes down to what people believe in. Some people believe that life starts at the moment of conception and others don't. Some people believe that life is sacred, others don't.