It is always best to go first for our answers to Jesus himself. He cried out on the cross, "My God, my God, why have you forsaken me?" It was a human cry, a cry of desperation, springing from his heart's agony at the prospect of being put into the hands of wicked men and actually becoming sin for you and me. We can never suffer anything like that, yet we do at times feel forsaken and cry, "Why, Lord?"
The psalmist asked why. Job, a blameless man, suffering horrible torments on an ash heap, asked why. It does not seem to me to be sinful to ask the question. What is sinful is resentment against God and his dealings with us.