Well we cannot totally justify with Ravana as here he represents the retrogressive movement in nature. He wants to undo what has been done through the centuries by the seers and sages. He wants to sow seeds of an aggressive and ambitious type of humanity whose focus is material and technological advancement at the expense of the spiritual side. His idea of liberty is licentiousness typified in the story of his sister Suparnakha and his own life led by lust and blind impulses. He cannot accept dharma since it means effort at self-mastery. He rather prefers to be driven by every impulse to satisfy his desire for selfish gains and personal pleasure.
And yet even Asura is an angel who has strayed from his true path. The Lord remembers and hence he assumes a earthly body to redeem and restore him to his divine origins which he has forgotten completely. It is this sublime love that leans down to rescue and redeem what is fallen and disturbed and distorted and release the divinity in it that we find in the Ramayana.
This Asura in man is typified in Ravana, once a devotee of the Lord who has hence fallen due to his lust for power and wealth and wanton ambition. Though the main antagonist in the plot, he is not a villain to be simply weeded out of existence, if such a thing were at all possible. Killing Ravana is becomes inevitable only because he refuses to change his ways. The chance is given even uptil the last moments but he refuses and insists on his doctrine of might is right and hence Rama must take the challenge and fight him on his own grounds. With the fall of the Asura and the conversion of the animal the path of humanity is secured at least for a few millenniums until the necessity for the coming of another Avatara arises.
Thus in the end by killing Ravana, Lord Rama shows his compassion as it liberates him and eventually he is converted to a Bhakta of Rama, thus we can say that Ramayana is also a story of transformation of a Asura.
Affectionately,
Alok Da
