I eat healthful foods because, while I may die some day, I plan on making that day an extremely long way away, and in order to enjoy living that long, I will need to be healthy. Being physically or mentally handicapped(morally handicapped, I can handle
) because you didn't eat right and exercise will make your life seem extremely long, regardless of how old you are when you die.
As for fats, you need fats to, among other things, lubricate your joints and transport fat soluable viatmins throughout your body. To be in balance, your diet should consist of 40% complex carbohydrates, 30% protein, and 30% fat, with less than 10% of that being saturated fat.