Would self interest be the dominant ethic when voting on issues within Interactive Democracy?
Though I don't doubt that this may be the core morality of some, I suspect the vast majority have some degree of empathy for others and aspire to live by the Golden Rule, which is at the core of most teachings about morality:
"What you do not wish for yourself, do not do to others... As you yourself desire standing, then help others achieve it; as you yourself desire success, then help others attain it." Confucius, c500BCE.
"So in everything, do unto others as you would have them do unto you, for this sums up the law and the prophets." Jesus, c30CE.
"Hurt no one, so that no one may hurt you." Muhammad, c630CE.
"The golden rule is a good standard which is further improved by doing unto others, wherever possible, as they want to be done by." Karl Popper, 1945CE.
And for many there is a voice of conscience, too. As Adam Smith wrote in his Theory of the Moral Sentiments (1759), "the man within the breast, the great judge and arbiter..." provides "the desire of possessing those qualities, and performing those actions, which we love and admire in other people; and in the dread of possessing those qualities, and performing those actions, which we hate and despise in other people."
The danger faced by any national democracy is that people feel small and impersonal in comparison to the scale of it, and they risk losing their empathy for other faceless souls, lost in the crowd. This is where leadership must come in. Especially leadership by those who can tell of their direct experiences of the topic to hand and how those issues have effected them; leaders who give political issues a human face.