Warnings from his masters were not enough. He believed his ancestors to be fools for sealing the move. So what if the technique could kill the person who executed it? The true warrior will do anything he can to win. And Akuma did. By releasing the Raging Demon, he sealed his evil destiny and destroyed his own master. Akuma trained with Gouken (Ryu and Kens Teacher). He ended up murdering gouken in a fight by a river, Ken and Ryu saw the whole thing and now seek to destroy Akuma.