Nietzsche and his existentialist philosophy might seem to be a little bit heavy for a blog about a rock n roll band, but Jim Morrison was an admirer of the German philosopher, and one of Nietzsche's works is arguably key to understanding what Morrison was trying to do.
That work is “The Birth of Tragedy,” Nietzsche's analysis of the roots of Greek literature as a dichotomy of two opposing forces- the civilized, beautiful and rational “Apollonian” side, and the intoxicated, dark and sexual “Dionysian” aspect.
Western literature has always had a place for this Dionysian side of art, which tends to the grotesque, chaotic and self-destructive rather than the calm, classical and serene. Nietzsche wasn't arguing that one was better than the other. In fact he argued that the greatness of ancient Greek tragedy depended on both aspects and the tense relationship between them.
For whatever reason, Morrison chose to incarnate the darkly ecstatic Dionysian side of rock n roll, without the balancing Apollonian aspect. He chose to emphasize the seductive glamor of intoxication and ecstasy, and much of the hypnotic power of the Doors' music stems directly from this deliberate imbalance, this appeal to the dark side. Darkness and ecstasy had always been aspects of popular music, but the Doors took these aspects and made them central, setting the stage for later developments from the Joy Division to the Cramps. In choosing to be Nietzsche's Dionysian artist, Morrison created the Gothic side of rock n roll