I can understand why someone would be zealously opposed to abortion. But it's been less obvious to me why someone would be zealously pro-abortion. I've been pondering it a bit, and this is what I think is going on.

Both sides would agree with the following:

  1. It is wrong to take the life of a human being
  2. If a foetus is a human being, then it is wrong to take the life of a foetus
  3. If a foetus is a human being, then a pregnant woman has no choice but to complete her pregnancy
  4. If a pregnant woman has no choice but to complete her pregnancy, she is not autonomous
  5. A pregnant woman is fully human

Then the sides go their separate ways...

"Pro-life":

  1. A foetus is a human being
  2. Therefore, it is wrong to take the life of a foetus (from 1, 6)
  3. Therefore, a pregnant woman has no choice but to complete her pregnancy (from 3, 6)
  4. Therefore, it is not necessary to be autonomous in order to be fully human (from 4, 5, 8)

"Pro-choice":

  1. To be fully human is to be autonomous
  2. If a foetus is a human being, a pregnant woman is not fully human (from 3, 4, 6)
  3. Therefore, a foetus is not a human being (from 5, 7)

I think the reason people are zealously pro-abortion is that they are deeply offended by what they perceive to be the suggestion that a pregnant woman is not fully human. And so they should be. But that stems from a particular view of what it means to be fully human. It's the view that to be fully human is to be an autonomous individual. If a pregnant woman is forced, against her will, to endure nine months of physical, psychological and emotional turmoil, it's really impossible to describe her as an autonomous individual. And, for those who believe that to be fully human is to be an autonomous individual, this means the pregnant woman is denied her full humanity.

So, for those who are zealously pro-abortion, it seems that the issue is really nothing to do with evidence. Instead, it's a matter of what it means to be human. Either the foetus is human, or the pregnant woman is human. It can't be both.