Maybe I missed something here, but why not just do cardio because it's good for you? It strengthens the heart and lungs, and makes the whole body function more efficiently. Our society has become so sedentery thats its ashamed, just because you look like your healthy on the outside, dosnt mean that you actually are on the inside. Being 230 at 6% bodyfat means nothing if you get out of breath walking to your car. In the words of the famous Jeep Swenson, "I never do cardio", by the way he also later died of a heart attack. Cardio is good for you no matter what the reasoning behind why your doing it, just do it.