Who said that? Some times humans think other humans have a responsibility to kill eachother; I'm guessing you sometimes agree.

Even if you believe humans should sometimes kill each other (which is not a universally held opinion, but also not insane) you should see all loss of human life as, at best, a necessary cost. To not consider enemy casualties as a cost goes against this. To not consider civilian casualties on the other side as a cost is even worse. If killing foreign people is not considered something costly, then war becomes too easy a choice for the countries with the most powerful armies.

Every heard of "human rights" ? They're not called "American rights" or "European rights", are they?