In my school days I have heard elaborate 'Ramayana' discourse by Thirumuruga Kripananda Vari Swamigal. He would devote a whole evening to the slaying of Vaali. There was one particular argument of Sri Rama that greatly appealed to me then and still more greatly now.
When Sri Rama mentioned his abduction of Ruma (Sugreeva's wife) as a great sin committed by Vaali, the latter (even in his dying moments) reportedly laughed that Sri Rama should know better and should not apply laws of human beings to Vaanaras who were not bound by such laws. Then the Lord told him that Vaanaras generally lacked the intelligence of humans and therefore this was not an immoral act for a Vaanara. But Vaali, Sugreeva, Hanuman and others were no ordinary Vaanaras and in fact they were greater Gnanis than most humans. Even if Vaali's abduction was not a crime by laws of Vaanaras, he (Vaali) knew that he was committing a great wrong and he should therefore not take recourse to such arguments to justify his act. Where the conscience is in conflict with the law the conscience should prevail. Vaali is said to have immediately accepted his guilt.