As the mental power works to gain control over the vital energy, there has to be a shift from the instinctive action of the vital to a more free exercise of the will. This provides both more scope for development and more need of discipline and restraint in order to direct and manage the energy effectively. The mental power includes morality and ethics as one of its lines, but these are not sole and fully determinative as there are actually a number of factors involved in achieving result in the world of action, and the moral force is just one of them.
Sri Aurobindo explains: “The moral is not the sole element: it is not entirely true that the moral right always prevails or that where there is the dharma, on that side is the victory. The immediate success often goes to other powers, even an ultimate conquest of the Right comes usually by an association with some form of Might.”
The concept of morality does play a part, especially in the interactions in society where we need the cooperation and good will of others, and the support of the framework of organisation of the nation and machinery of government in order to succeed. In this instance, any willful disregard of the moral aspect can lead to opposition and cross-currents that would inevitably weaken, or even defeat the goal of the effort. As a result there are automatically checks that make it difficult for someone to use the mental power to gain control over the vital and physical life to an extreme degree.
“Moreover, man in the use of his energies has to take into account of his fellows and the aid and opposition of their energies, and his relations with them impose on him checks, demands and conditions which have or evolve a moral significance. There is laid on him almost from the first a number of obligations even in the pursuit of vital success and satisfaction which become a first empirical basis of an ethical order.”
Sri Aurobindo, Rebirth and Karma, Section II, Chapter 15, Mind Nature and Law of Karma, pp. 133-134, http://www.lotuspress.com/item.php?item=990117