I don't know if I agree with you there, Nothing. David never necessarily screamed "pure evil" from the start. He was a little troubled and bratty, but that could have fixed itself in time. Besides, the Animorphs have all done things that were cruel or outright surpassed David's actions, like Cassie erasing a man from existence, Tobias killing off the Mercora race, Jake killing off 17,000 Yeerks, and if Marco had killed Karen, I'd include him in this list too. And they all worked out. I'd say in the end, it was a series of circumstances that doomed David, most of which were the Animorphs' total inability to commit to David. I get Mrs. Applegate wanted to make it look like Marco was justified in hating David, but the way I see it is that was part of the problem that led to him rebelling in the end, just like Jake forcing David to sleep in a freezing barn instead of putting him with the Chee or God forbid, just letting David sleep where he wants. Then again, the Animorphs were rushed to save the world leaders. Imagine if there was no ticking clock. Could things have worked out? Would they have been better willing to commit to David and see the problems he was having?