You said the state has the authority to allow one person to take the life of another when that person believes the other poses a threat to him - which necessarily includes the case of a person who reasonably, but wrongfully, believes that his life is in danger. You can't have it both ways.
Actually, just the opposite. The right to defend your life is a fundamental right, not something a state 'allows'.
Where we get into the abortion debate, imho, is beyond a conversation of self-defense (as I said in a previous post, this is something I just don't know regarding the level in the life of the mother issue). Very few will argue that most abortions are for protection of the life of the mother (self-defense). A vast majority of those performed are for convenience. This is where I feel a State, nor any governing body, doesn't have the authority to let strip a right of one individual for the convenience of another.
If we weren't talking about the unborn, it wouldn't be so vague. What if one State decided that a toddler who causes the mother so much stress she may develop a heart condition could have his life forfeit to her? What if another State decided an elderly parent's life is forfeit to the children who have to help provide for them because it may create undue stress on them?
What if it wasn't life? What if it was property? What if a State decided your home would be better served to the community to give it to a shopping mall developer.
How much more important is life yet both are (
should be) protected from a State (or any governing authority) power.