There are other arguments in favour of a rational basis for personal
ethics. Let's start by assuming that everyone wants to optimize their
own prospects in social or market exchanges. On that basis, we can
consider life as a rather more complex version of a classic iterated
prisoner's dilemma. To recap: if two people cooperate, they get a small
payoff. If one cooperates and the other defects, the defector gets a
small payoff and the cooperator is stung. If both defect, they both get
stung. Now make this a repeating situation, where both players can
remember the other's previous behaviour: it turns out that the optimal
strategy is to always cooperate _unless_ in the last round the other
player stabbed you in the back. But don't hold grudges -- if they
start cooperating again, follow their example.
Apply this principle in general and you get something not unlike the
"golden rule"; do unto others what you'd like them to do until you (but
don't turn the other cheek if they spit in your eye).
Is it rational to want to base your ethics on a game-theoretical
approach to maximizing prosperity?
-- Charlie