The body's metabolism wears on you very hard relative to other things. Simply put, it has been shown that the more you eat, the sooner your body will break down. More food=shorter life. It sounds silly, but its true. personally, I'm willing to shave a few years off the end of my dull old man life to live big and happy with myself.
The reality is, the very nature of our lifestyles as bodybuilders makes us healthier than the people barking about our diet regardless of how much we eat.