If humans have value, then abortion must be immoral. Here’s why:

Value is either intrinsic (part of the nature of the thing itself) or extrinsic (conferred on a thing by an external source). If value is intrinsic to human beings, then humans are valuable the moment they come into existence. Since it is a scientific fact that human beings come into being at conception, then unborn humans have the same value that you and I have from the moment of their conception. As such, it would be just as immoral to kill an unborn human as it is a born human. So if you believe humans have intrinsic value, then you should be opposed to abortion.

Most thoughtful pro-choice advocates think human value is extrinsic rather than intrinsic, meaning humans are only valuable if someone else finds some sort of instrumental value in them, or if they meet some sort of subjective criteria for value that others have created (such as consciousness, self-awareness, etc.). When applied to the unborn, this means the unborn human only has value and only deserves legal protection from harm if his/her mother wants him/her. If she doesn’t want him/her, then the unborn human has no value and can be killed.

This is problematic. If an individual human being is only valuable if some other human being attributes value to him/her, then every human can be killed – both the born and the unborn. A 20 year old female has no value unless someone finds something instrumentally valuable about her. If we can kill any human that is without value, and if any human’s value is dependent on another person’s valuation of him/her, then any human being can be killed by any other human being (regardless of age or location) so long as the latter human does not value the former. An extrinsic view of human value not only justifies abortion, then, but also the murder of every born human being. So if you hold to an extrinsic view of human value and you wish to be consistent in your thinking, you’ll either have to condemn the killing of both born and unborn human beings, or permit both. Only the morally insane would permit both, so even if you believe human value is extrinsic, you should be opposed to abortion.