First, there is no way of telling if five lives are worth more than one, there is no telling if its even morally justified to sacrifice some to save more, and there is no telling just who gets to decide that when such decision has to be made, is it a truly moral and capable agent?
Second, even if this logic worked in theory, it has rarely worked in practice. This logic was merely used to justify countless wars, crimes, and countless of bad economical policies which in the end actually achieved opposite of what logic originally intended.
Third, people who calculate too much regarding morality always produce inevitable result of miscalculation and when more groups and countries do calculations of course their calculations dont match, producing conflict.
So even if principle was true morally, practically its still an epic failure, because people are not morally good and the idea that they wont abuse the shit out of such a principle which offers countless ways of misuse, is silly.