First of all, I disagree with the entire premise of the question. Why does the intelligent have an obligation to dedicate his or her life to the creation of maximal value for society? Sounds like Nietzsche's slave morality to me. Why does the attractive/tall/healthy not have a similar special moral obligation? Second of all, providing liquidity is very important. Sure, you are only shaving off a few basis points, but…
What does intelligence have to do with it? Sweeping the streets is an honorable job and makes the world a little nicer. Writing a botnet for spammers isn't and doesn't.