When Neil is being held hostage by Grant, why didn't he, in one of the times when his arm was free, say something like "Grant die", or something else quick and effective? He could easily have gotten free. Hell, even if Grant killed Dennis, he could easily have revived him.
Considering that Dennis is still able to speak, this means that all previous wishes still remain, including the grand canyon in Catherine's office!
When Catherine thinks Neil is gay with his "brother", Dennis, and she storms out in disgust, why doesn't he just wipe her memory of that? He clearly has no qualms about doing such a thing as he made her forget him perving on her earlier.
Okay, so Neil's first attempts at making the world better failed due to imprecise wording. He didn't think to just specify "Replace global warming with a healthy atmosphere" etc. instead? It's not like he couldn't undo any other failures until he got it right.
If the aliens believe that weakness is evil and destruction is good, then of course nobody's passed the test - any good person would not have used the powers for destruction (at least, not intentionally), while any evil person probably wasn't destructive enough for the aliens' liking.
An additional reason why nobody has passed the test is that it is likely that anyone destructive enough for the aliens' liking would manage to get themselves killed as collateral damage of their own wishes.
