In the play The Crucible, what elevates the circumstances of the play from a melodrama to a tragedy?

A melodrama is a sensational dramatic piece with exaggerated events and characters designed to appeal to the emotions. One feature of melodrama is that characters tend to be what are often called "whole" characters, that is to say wholly good or bad, weak or strong, innocent or guilty. There's no nuance or subtlety to such characterization. If we accept that The Crucible is indeed a tragedy, then we can see how it rises some way above the comforting certainties of melodrama.
In the central figure of John Proctor, a tragic hero, we have a divided character, torn between conflicting impulses and ultimately brought low by a fatal flaw. He undergoes a profound inner conflict, struggling to reconcile his religious convictions with the overriding need to speak out and do what's right. Far from being a whole character, John is sharply divided, the shards of his fractured soul mirroring an increasingly atomized society in which everyone is at each other's throats.
The Crucible deals in considerable depth with the full range of complex human emotions and human psychology. Its deft brush strokes provide us with delicate hints of gray rather than the bright primary colors of melodrama. It appeals to our emotions, yes, but it also makes us think. It gives us pause to reflect, not just on seventeenth-century Salem, nor even just 1950s America during the McCarthy witch hunts, but on ourselves, our values, and the society in which we live. Because of its subtlety, nuance, acute psychological depth, and intellectual heft, The Crucible can never seriously be described as a melodrama or anything of the kind.