My college tutor once confronted us with the following ethical dilemma:-
A fire is raging in an art gallery. You rush in, knowing you have only a few minutes to save a unique and very valuable painting. But in the hall you find a drunken and smelly old tramp, who has sneaked in to doss down for the night. You do not have time to save both the tramp and the painting. What should you do?
This rather improbable scenario was intended to make us think about utilitarian ethics. Which should be considered more valuable: the life of a socially worthless individual, or an irreplaceable artistic masterpiece - a Rembrandt, let us say? (You can, if you wish, substitute "dog", or indeed any other word, for "painting")
I always think it is useful, in dealing with such questions, to ask what that rather underrated political philosopher Adolf Hitler might have said. Hitler, I'm sure, would argue that it depended upon the tramp's race: if he was a negro or a Jew we should certainly not bother to save him. If he was an Aryan, it might depend on his background: if he was a war veteran who had fallen on hard times, he deserved to be saved out of gratitude; but if he was simply a life-long derelict, then not. Stalin or Mao would surely have abandoned the tramp to his fate as being economically worthless.
I would deduce from this a utilitarian argument: I would not wish to live in a society in which someone in a position of power could decide that my life was less valuable than a painting (or a dog), perhaps on grounds similar to those cited above, or on others equally reprehensible to me. I do not see how this could ever be in my interest. I am, of course, always free to decide for myself that my life isn't particularly valuable ("Don't worry about me: save the Rembrandt!" - or, alternatively, "save my dog!"); but I don't want someone else unilaterally to make this decision for me. That is how dictators and conquerors have always treated the mass of the people - even their own subjects.
In principle, then, we must always treat the preservation of human life, any human life, as being of supreme importance.