An argument against euthanasia asserting that mercy killing would involve treating persons as mere things and of no more value than of a beast draws on "Kant’s categorical imperative".
The Categorical Imperative should give an approach to us to assess moral activities and to make moral judgments. It's anything but a charge to perform particular activities - it doesn't state, "take after the 10 instructions", or "regard your senior citizens". It is basically "exhaust" - it is just formal technique by which to assess any activity about which may be ethically important.