Christians should know better than this. You can't relieve yourself of responsibility and absolve yourself of guilt with legalistic sophistry. You say you're morally against abortion but politically prochoice. This stratagem may be clever politics, but it's moral nonsense. I've never heard of anyone morally against theft, assassination and rape but politically prochoice on the actions of thieves, assassins and rapists.
Abortion is no different.
The only reason to be morally opposed to abortion is that kills an innocent human being made in God's image. And since it does precisely this, it should be banned. It is the God-given duty of the state to protect every human being's right to life. It is our solemn obligation to use our political rights to move the state to do its duty. Our duty is clear.