Here's where moral relativism comes into play.
Sure, I can do the math and say 5x > x. But I feel that to take that as an absolute is purely intellectual and, well, disingenuous. What is x, the variable? Is it merely the number of bodies? Is it emotional involvement, personal expreience, cultural identity, the value of a human life? Or something completely different? Just for the sake of argument, if x = 0, the above equation is false.
>but i know you and i share something in common: we're both human. how can you not feel that?
I see this as a plea to your own set of morals, to which I may or may not subscribe. This statement assumes that I place the same value on human life as you, and that this value is absolute. But it's not that easy. To use a cliché example, samurai in ancient Japan believed that taking one's own life was the best way to restore one's honor. Does that mean that the Japanese place less value on human life than Westerners? (Incidentally, answering this question with an affirmative was a popular piece of propaganda during WW2.)