abortion is more evil than contraception is because it's an error of commission rather than omission.
I think taking birth control precautions is pretty comission-y. Abstinence would be the omission version of not having babies.
After reading the entire debate this comment spawned... if the goal is to determine whether we should support abortion legalization and fewer restrictions (possibly up to infanticide? (!)), or perhaps support more heavy regulation, it seems like arguing over whether an action is reactive, proactive, etc can't possibly have any relevance, and seems like a particularly virtuist way of looking at things.
Are we not solely interested in consequences? What are our values and how do we maximize them? Clearly saying we value "human life" isn't enough, an...
A few years ago, I wrote a little dialogue I imagined between 2 materialists, one of whom was for and one against abortion, centering on the personal identity question. I recently cleaned it up and added a number of references for the biological claims.
You can read it at An Abortion Dialogue.
Early feedback from #lesswrong is that it's a 'nicely enjoyable read' and 'quite good'. I hope everyone likes it, even if it doesn't exactly break new philosophical ground.