94 For as the Apostle with good reason admonishes us: "Those that seem the more feeble members of the Body are more necessary; and those that we think the less honorable members of the Body, we surround with more abundant honour." Conscious of the obligations of Our high office We deem it necessary to reiterate this grave statement today, when to Our profound grief We see at times the deformed, the insane, and those suffering from hereditary disease deprived of their lives, as though they were a useless burden to Society; and this procedure is hailed by some as a manifestation of human progress, and as something that is entirely in accordance with the common good. Yet who that is possessed of sound judgment does not recognize that this not only violates the natural and the divine law written in the heart of every man, but that it outrages the noblest instincts of humanity? The blood of these unfortunate victims who are all the dearer to our Redeemer because they are deserving of greater pity, "cries to God from the earth."
Source: Mystici Corporis Christi (Vatican.va)