You know it's an interesting question.
Klaatu has to answer the ultimate question: does human species deserve to live because of it´s impact on the rest of the planet´s species ... ?
Suppose alien life came to this planet and re-educated every single human being to no longer fight and destroy. I wonder how long it would take for humans to go back to their old ways... I'd give it a couple hundred years at most.
Seems to me there are certain strands of DNA that simply aren't wired right and unfortunately there are a number of humans inhabiting this earth that have these genetic sequence or defects, only these people don't see them as defects, they see them as what makes them superior to others. And because of this self-proclaimed superiority, these people put themselves first above all others. That's when it all breaks down and begins to regress to a caveman like society. History shows that once a society comes apart, those that claim to be superior simply run off to some new place and start over. They never stick around and try to fix the problem, because that would entail them fixing themselves, which I do not think can be done. They probably know that too.