This is uncharacteristic of Mega Man to this point in the series, but it makes sense given a tragic interpretation. Mega Man has had to kill 54 of his fellow robots through his battle with Wily, and by carrying their data he is unable to become desensitized to the violence. Wily waving Mega Man's inability to kill humans in his face is an assault to all the suffering Mega Man endures to that point, as it implies that robots aren't as worthwhile as humans are. "I am more than a robot!" is a line that I take to mean that Mega Man acts, thinks, and suffers like a human does, and this enrages him because Wily is clearly unable to see this as he continues to manipulate robots for his own desires.
I could easily go on, and I'm sure there are certain bits in the series that might contradict this particular interpretation, but that's part of the appeal. While this may be "my" Mega Man, the same character doing the same things can mean something completely different for another player. This is what keeps Mega Man relevant as a character, and the fact that the games tend to be fun to play certainly has a lot to do with it as well. Mega Man is more than a robot. He's an icon made up of equal parts awesome, nostalgia, and ourselves, and I can't wait to be able to throw metal blades in Donkey Kong's big goofy face in 2014.
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