But it's how language actually works, though not in quite such an arbitrary way as Lewis Carroll mocks here. The way words are used changes, getting broader or narrower, and dictionary definitions trail along behind keeping up.
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Murderers generally consider the lives of their victims as "of a lesser value than their own". And yes, Murder is Murder.

But equally "War is War" - but that does not mean that when we should avoid talking terms like the Great War, and World War II and the Korean War, but should always say "the Great War". Distinguishing between different wars makes it possible to discuss them, and to explore their causes and effects. It doesn't imply that we are diminishing the importance or horror of the different wars or placing them in some kind of ranking order.

The same is true of the episodes of genocide that have punctuated our history, and continue to do so.