I'm aware of OSC outside his books, but within Ender's Game there is an exploration of a topic. It is the height of hubris to present one interpretation of fiction as if it is the only one and true one. I never read the book as excusing the genocide, rather that the horror of it was a major point. Is Ender innocent of genocide if he didn't know he was committing it? I don't know, that's a thought experiment and discussion topic, but not one that I read excusing the genocide itself.

I find the linked page leaning heavily on the moral judgements and particular language of Graff, a character who I never found trustworthy or to be taken at face value. He always seemed to be saying whatever he needed to say to smooth past uncomfortable situations so he could mold Ender as he wanted him to be. Like he was an authority figure in some kind of dystopia.