So why did they not...?
Destroy human life?
"There is another side to you" Really? What happened? Apparently Jennifer Connelly's character did something so profound that they go from killing every human on the planet to sparing us. All I recall was her and another fellow scientist driving him to Central Park and her pleading to save the boy.....she also comforted him at the cemetery. Was that it? I mean, they appeared to know a lot about humans......I'd assume they know most humans are protective of their young. Seeing mom (step-mom) concerned about their child shouldn't have been shocking to them.
So, what occurred in that last 10 minutes that caused the change? "There is another side to you."?
I thought the most convincing persuasion was the scholarly scientist man saying.....we are at that point now, give us a chance to change as you did. That was more convincing than any of the other stuff.