The problem with the morality test... (SPOILERS)
is that it is black and white, draconian, and lacks the capacity for subtlety, nuance, or extenuating circumstances. Even our laws and ethical codes do not always state "To kill is wrong." Think about war; self-defence; our police forces; the death penalty; euthanasia. These are all moral/ethical grey areas, and may differ according to culture or personal belief.
So the human race is being tested by means of the box (not a very efficient or conclusive test, to be sure, based on the number of boxes, time taken for the test to run out, and eventual judgement on the morality of just 2 of the world's 7 billion people). Pressing the button means you fail; not pressing means you pass. It's a black/white, binary choice. But it leaves no room at all for individual circumstance.
At the most obvious end of the spectrum, you have financial need. A billionaire would have no need to press the button as the million dollars would be nothing to him. So, according to the test, he passes and is "moral". But what if he is a total b*stard, cruel to his wife and children, has affairs, kicks his dog, etc? Still, he passes the test and is left in peace. On the other end of the spectrum, a homeless couple, living in a filthy unsafe hostel, with a kid with chronic bronchitis from the damp in the walls? You bet your butt they'd take that million to save their own kid. Does that make them immoral? According to the box test, yes. They "fail" the test. And suffer the consequences.
And there are any other number of reasons that people might press the button. Disbelief in its authenticity (as has been discussed elsewhere on this board). Neurological or mental health conditions which affect impulse control. Being under the influence of alcohol or drugs. Crippling debt which you have hidden from your family. Pressure from a (possibly abusive) spouse. There are so many reasons why someone might feel or be compelled to press the button, but that doesn't necessarily make them immoral. Just in the same way that a person can kill in self-defence and get acquitted by a jury. But here it is all reduced to the overly-simplistic Push=Bad, No Push=Good.
The way it's presented in the movie, we humans are supposed to be the less-evolved species, needing to be tested and taught a lesson. On the basis of this test, I have my doubts.