So we are back to where we started. Debate!

"The baby is not considered to be a human life until brain activity develops, therefore the baby is part of the woman's body, therefore she can do as she wishes up until brain activity begins."

If you say that the baby is life from conception (belief in a soul, which is irrational anyways), then you must also be completely pro-life by default. Just letting you know. And believing that the baby is a life from conception is the only way you could say you have responsibility for it too.

If you disagree with the existence of the soul, Saying you are equally responsible for the baby is equivalent to saying "Look, I gave you these boob implants, now you will allow me to have them removed if I wish to do so in the future." It would be equal to having unfair control over the woman's body.