Ravana was so sinful and shameless that he did not know what the result would be of kidnapping mother Sita, the pleasure potency of Ramacandra. This is the disqualification of the Raksasas
SB Canto 9
Lord Rāmacandra said to Rāvaṇa: You are the most abominable of the man-eaters. Indeed, you are like their stool. You resemble a dog, for as a dog steals eatables from the kitchen in the absence of the householder, in My absence you kidnapped My wife, Sītādevī. Therefore as Yamarāja punishes sinful men, I shall also punish you. You are most abominable, sinful and shameless. Today, therefore, I, whose attempt never fails, shall punish you.
Na ca daivāt paraṁ balam: no one can surpass the strength of the Transcendence. Rāvaṇa was so sinful and shameless that he did not know what the result would be of kidnapping mother Sītā, the pleasure potency of Rāmacandra. This is the disqualification of the Rākṣasas. Asatyam apratiṣṭhaṁ te jagad āhur anīśvaram (BG 16.8). The Rākṣasas are unaware that the Supreme Lord is the ruler of the creation. They think that everything has come about by chance or accident and that there is no ruler, king or controller. Therefore the Rākṣasas act independently, as they like, going even so far as to kidnap the goddess of fortune. This policy of Rāvaṇa's is extremely dangerous for the materialist; indeed, it brings ruin to the materialistic civilization. Nonetheless, because atheists are Rākṣasas, they dare to do things that are most abominable, and thus they are punished without fail. Religion consists of the orders of the Supreme Lord, and one who carries out these orders is religious. One who fails to carry out the Lord's orders is irreligious, and he is to be punished.