Harold Goddard's The Meaning of Shakespeare (1951) contains many highly original insights. The one I'm concerned with today is his contention that the turning point in Hamlet actually occurs during the play-within-the-play scene. At this point, Hamlet has not yet killed anyone (whereas by the end of the play, he's directly responsible for five deaths, and not quite as directly, for two others - three if you include his own), so theoretically the story could still end happily. Goddard states that the key moment is when Hamlet decides to not simply let the play do its work, but rather to intercede with a running commentary (maybe Shakespeare was taking a jab at critics). The actor playing Lucianus is about to act (or reenact) the murder, by pouring poison in the ear of the king, when Hamlet makes his fateful interjection:

LUCIANUS

Thoughts black, hands apt, drugs fit, and time agreeing;

Confederate season, else no creature seeing;

Thou mixture rank, of midnight weeds collected,

With Hecate's ban thrice blasted, thrice infected,

Thy natural magic and dire property,

On wholesome life usurp immediately.

(Pours the poison into the sleeper's ears)

HAMLET

He poisons him i' the garden for's estate. His

name's Gonzago: the story is extant, and writ in

choice Italian: you shall see anon how the murderer

gets the love of Gonzago's wife.

OPHELIA

The king rises.

Goddard's position is that the court would not see the king rising as an admission of guilt, but rather that the prince's lunacy had reached an intolerable point, thus occasioning the king's departure. And that, left alone, the play would have perhaps had the effect of working his conscience toward confession, maybe even abdication. We'll never know. Goddard brilliantly sums up the two warring states in Hamlet at this point by invoking Blake's phrase, "Art Against Empire". Of course, this theme is dealt with throughout the sonnets, as well; see 65 for a particularly pertinent example.