Former Christian here.

This is it. Criminals have (theoretically) been proven guilty. Some crimes are worthy of death.

A fetus (ahem unborn baby) has cast no sin and does not deserve death.

Christians would also say that they would never get out to death because they would never do anything wrong but when you bring up the fact that Jesus himself said you should be willing to suffer even to the point of suffering on a cross, they start changing the subject.