The CWCki covers this somewhat, but allow me to fill in a few more blanks on that.
Sonichu was the one thing Chris had in his life that he had ABSOLUTE control over, which, for an autistic person (who generally find change they can't adjust to abhorrent) who desired some form of control over his life, to be very comforting.
It was also the one realm he had power over his enemies.
And then he felt that he lost that power when he felt compelled to kill a character in his fantasy world to make the trolls go away.
His last refuge against an otherwise uncontrollable world was no longer inviolate, it had been compromised, and while his vapid recolors and stolen ideas are shallow to us, they mean something to Chris, and his having to kill off a crap character in his bad webcomic was for him traumatizing because he had to invade his sanctuary and kill one of its residents to please the world he couldn't control.
He had to invade his own personal hugbox and hated himself for it ever since.