Assuming that Hamlet should obey the ghost

During the last two centuries, the predominate thinking on Hamlet has been based on the assumption that Hamlet should have obeyed the Ghost's command to revenge his father's death. Given this assumption, then, the essential question has revolved around the reasons why it took four more acts to accomplish the task assigned to him in Act One.

Here are a couple examples of theories that assume that Hamlet is justly compelled to revenge, and wonder at his delay.

Surely it is clear that, whatever we in the twentieth century may think about Hamlet's duty, we are meant in the play to assume that he ought to have obeyed the Ghost. --A.C. Bradley, Shakespearean Tragedy. New York, Meridian Books, 1955. p.87

A voice from another world, commissioned it would appear, by heaven, demands vengeance for a monstrous enormity, and the demand remains without effect; the criminals are at last punished, but, as it were, by an accidental blow, and not in the solemn way requisite to convey to the world a warning example of justice...-- August Wilhelm von Schlegel, Lectures, trans. J.Black, London 1846.

And when the ghost has vanished, who is it that stands before us? A young hero panting for vengeance? A prince by birth, rejoicing to be called to punish the usurper of his crown? No!  --J.W. von Goethe, Wilhelm Meister's Apprenticeship, trans. T. Carlyle, 1824.

It was common for Twentieth-Century critics to assume that while revenge is condemned by modern law, it was condoned in Elizabethan society. Here's just one example.

When Shakespeare wrote this play revenge was part of the moral law for many minds: failure to avenge a murdered father was as unnatural as irreverence to God, disloyalty to the King, or any other refusal to acknowledge the natural bonds of blood and sanctity of an ordered universe.  --Bertram Joseph, Conscience and the King, Chatto and Windus, London, 1953, p.40.