Argument: Euthanasia is contrary to the dignity and preciousness of life
Patrick Lee. "Personhood, Dignity, Suicide, and Euthanasia". The National Catholic Bioethics Quarterly. Autumn 2001, Vol.1 No.3 - "Why Suicide and Euthanasia Are Morally Wrong
There are various arguments against suicide and euthanasia. For example, one might argue that such acts violate God's dominion. Here I will argue that the reason why suicide and euthanasia are wrong is that they are choices contrary to the intrinsic good of a human person. Such acts are contrary to the love of God, neighbor, and self that is the objective moral standard of our choices under the natural moral law that is evident to reason.2
When one chooses an action, one chooses it for a reason, that is, for the sake of some good one thinks this action will help realize. That good may itself be a way of realizing some further good, and that good a means to another, and so on. But the chain of goods cannot be infinite. So, there must be some ultimate reasons for one's choices, some goods which one recognizes as reasons for choosing which need no further support, which are not mere means to some further good.
These ultimate reasons for choice are intrinsic goods, that is, conditions understood to be good for their own sake, and not just as means to some further end. What these goods are is not determined by choice, since they make choice possible. Hence these goods have a natural appeal to us; they must be activities or conditions to which we are naturally inclined. Moreover, these goods are conditions that can be realized by our actions. Thus, these fundamental human goods are the actualizations of our basic potentialities, the conditions to which we are naturally oriented and which objectively fulfill us, the various aspects of our fulfillment as human persons. To choose in a way that respects all of these human perfections, both in ourselves and in others, is to respect human persons and to choose morally well. It is to act in a way that is consistent with love of God, neighbor, and self.3 To choose to act against a fundamental human good is to act against some intrinsic good of a human person. To make such a choice is to substitute one's own preference for the objective standard provided by what is objectively fulfilling.
Human life itself is a fundamental human good. Thus, we ought to respect this good.4 But the choice to destroy a human life is contrary to respecting human life. And so, we ought never to choose precisely to destroy a human life, whether of another person or our own. To do so is implicitly (and sometimes explicitly as well) is to adopt the attitude that this human life is not objectively good, but is good only if I desire it. To choose to destroy one basic good for the sake of others is to adopt the attitude that human goods, including human lives, are only conditionally good. It is to adopt the attitude that the goodness of this life, for example, can be outweighed by the good consequences (or avoidance of bad consequences) one would bring about by destroying it. It is to adopt the attitude that, in effect, a price can be placed upon this life. But the intrinsic goods of persons, including life itself, which is the very being of the person, are irreplaceably good; each is a good whose loss cannot be made up for by some other condition. Every human life is priceless.5
Thus, the choice to kill an innocent human life, whether one's own or another's, even for the sake of avoiding terrible suffering, is intrinsically immoral. Euthanasia and suicide are contrary to the intrinsic dignity of human persons."