That's a hard question to answer, since, let's face it: ethics differ from person to person.
For me, at least (even though I know you didn't ask for mine, but that's just tough
), ethics stem from my belief that each individual's purpose in life is to serve one another - and by serving each other, we will be rewarded - not just in the next life, but in this life, as well. Now, since we're imperfect beings, it's impossible to do that consistently or adequately, and besides that, we aren't always afforded the opportunity to be altruistic. Also, let's face it: folks don't always do unto others as they would have done to them. They won't always scratch your back just because you scratched theirs.
But here's the beautiful part of it: doing your best, and being able to say to yourself, "I did my best, regardless of how it turned out," is its own reward. John Wooden, the legendary coach of the UCLA basketball team in the 70's, got me hooked onto this line of thinking when I saw him speak at my school last year (Occidental College). Taking the path that avoids regret is my way of both making myself happy and doing the ethical thing; if I can say in all honesty that I've done my best, then what can I possibly regret?
This isn't a call to aesceticism, mind you; although our primary goal should be to serve others so that our needs will be cared for in return, this doesn't mean that we shouldn't take care of ourselves, where needed. After all, what good are we to society, to our fellow man, to the love of our life, to our children, to God - in short, to whomever we serve - if we allow our body, or our mind, or our spirit, to fall into a state of decline?
Anyway, that's why I believe one should be ethical: because, as Plato argues in
The Republic, it's simply satisfying to be good to others, and it's unsatisfying to be unjust.
This fits in perfectly with the DJ philosophy; in fact, it's about the biggest confidence booster I can really imagine, knowing that doing my best is not only satisfying, but also a goal that I can definitely attain.