Human life is sacred because of the relationship of human persons to God. God makes human persons in his own image and prohibits killing them. Life is a human person’s concrete reality, and bodily life is an intrinsic good of persons. No bad condition can lessen its goodness and sanctity.
It is always gravely wrong to intend to kill the innocent, either as an end or as a means. (Innocent is a technical term referring to everyone except those found guilty of capital crimes and enemy combatants in war.) Catholic tradition and the magisterium exclude all exceptions; and this prohibition extends to suicide and euthanasia. Intentionally killing the innocent is always grave matter.
Sometimes, however, though by no means always, it is morally acceptable or even obligatory to accept death or the risk of death as a side effect. (Choosing precisely to risk death, however, is never morally acceptable, since that is choosing to kill.) It is in this context, morally speaking, that deadly force sometimes may be used for defensive purposes. Its use, nevertheless, is limited by fairness and mercy.
The Church’s affirmation of the personhood of the unborn is reasonable, while arguments against their personhood are not persuasive. Since every human individual should be treated as a person from fertilization, the moral norms protecting others’ lives apply to the unborn. Abortion is morally excluded not only when it involves intentional killing (as it generally does) but also, ordinarily, even in the small number of cases when the child’s death is accepted as a side effect. Some methods of so-called contraception are in fact abortifacient and are to be rejected along with other forms of abortion.
But even true contraceptive acts, considered in moral terms, are contralife, since one who chooses to contracept chooses to prevent a new instance of the basic human good of life. Thus, contraception is always wrong, and choosing to use contraception is grave matter.
Health is not pleasure and felt satisfaction, nor should the idea of health be expanded to take in total human well-being. Rather, health is well-integrated, harmonious, psychosomatic functioning. One should take reasonable measures to protect and promote health, both one’s own and others’, especially one’s family’s. In deciding whether to accept or reject medical treatment, the benefits and burdens should be evaluated by moral standards, and the decision should be made in light of personal vocation. Psychoactive substances should be used rightly—to promote healthy functioning—and should not be abused.
There also are various other responsibilities toward persons as bodily: to maintain bodily integrity in harmony with health (sterilization as a method of birth control always is wrong, but organ transplants can be right or wrong, depending on their relationship to relevant goods); not to engage in sexual assault, which always is grave matter; to shape all other bodily contacts by justice and charity (this rules out prizefighting and any other intentional bodily injury in sports); and to respect the space and mobility of other persons.