HAMLET: Then trip him, that his heels may kick at heaven... This speech in which Hamlet, represented as a virtuous character, is not content with taking blood for blood, but contrives damnation for the man that he would punish, is too horrible to be read or to be uttered.  - Samuel Johnson, On Shakespeare, Penguin, London. 1989. p.242.

Samuel Johnson represented the last of an old breed that disappeared from view with the coming of the 19th. Century. His assumption that Hamlet hesitates to act in the murder of Claudius for moral and ethical reasons was supplanted by the view that any hesitation was purely psychological. Samuel Taylor Coleridge served as the spokesman for the new voice in writing his rejoinder to Johnson

Dr. Johnson's mistaking of the marks of reluctance and procrastination for impetuous, horror-seeking, feindishness! --Of such importance it is to understand the germ of a character.  - Samuel Taylor Coleridge, Writings on Shakespeare, Capricorn, N.Y. 1959. p. 153.

For this generation, there is no consideration about the ethics of revenge, nor about the possible demonic inspiration of the ghost. They clearly believed that the ghost's urgings comprised an unquestionable imperative to action, and that Hamlet recognizes his duty to complete the task assigned to him by the spirit of his deceased father.

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 the solemn way requisite to convey to the world a warning example of justice.  - J.W. von Goethe, Wilhelm Meister's Apprenticeship, (tr. Thomas Carlyle) in The Romantics on Shakespeare. p.310. There is no indecision about Hamlet as far as his own sense of duty is concerned; he knows well what he ought to do, and over and over again he makes up his mind to do it.  - Samuel Taylor Coleridge, Writings on Shakespeare, Capricorn, N.Y. 1959. p. 161.

The entire issue for the Romantics, and for the majority of Shakespeare critics of the last two centuries has been the question of why Hamlet needs four more acts to complete the assignment given to him by the end of the first act of the play. They see the play as an engaging study of the psychological mechanisms of resistance which manifest themselves in Hamlet's apparent hesitation to kill Claudius. For them, it is clear that Hamlet knows what he must do at the beginning of the play. The question is, "what psychological flaw motivates his delay in doing it, and how does he overcome his internal resistance?" Needless to say, the answers to that question have been numerous, and they tend to change as new psychological theories come into popularity or fade from it.