Doctors' judgement isn't perfect
Legalizing euthanasia could prevent some patients from possible, even if unlikely, recovery.
The Sanctity of human life is an idea, that human life has an inherent, non-relative value which should be protected and by no means violated for any reason, with exception of self-defence or defence of others. It's a major component of virtually every major religious tradition and the basis for human rights.
The human life is sacred, irrelevant of its worth for the society, the market or its general usefulness or self-reliance. We cannot differentiate between "better" or "worse" lives based on its quality. Every human being should be treated as an individual, whose well-being and right to live is of the utmost importance, no matter what affliction ails them. The legal euthanasia cannot be accepted in the light of this view since its most basic premise - that there are some lives not worth living anymore because of a suffering or an illness - undermines the sanctity of human life, which can have profound and undesirable consequences for the way we think about ourselves as human beings.
The Sanctity of life is not an absolute law, which is visible in how many societies have permit the capital punishment or even passive euthanasia. It also imposes certain moral considerations on individuals, who might no subscribe to them.
The human life is sacred. Euthanasia undermines this claim by the premise, that life can become not worth living. Therefore, a legal euthanasia cannot be reconciled with the sanctity of human life.
The sanctity of human life is not a universal view and often gets ignored in some contexts, most noticeably in the discussion of the capital punishment, where the view that some lives should be ended for the good of society is a commonly used an argument.
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