Cоnsider the fоllоwing аrgument:"Physiciаn-аssisted suicide of terminally ill patients who are experiencing severe pain is morally wrong because killing oneself out of concern for oneself (destroying one's life for the purpose of improving one's life) is inconsistent and thus cannot be turned into a universal law of nature. Besides, killing oneself just to stop the pain is to use oneself as though one were a mere object." Which of the following theories best fits the reasoning in the above argument?