Fruit is not bad for you. I don't care how much sugar a banana has in it, it is not going to affect your body the same way a chocolate chip cookie will. When you eat a cookie, your body has a very quickly elevated blood sugar level, giving you a burst of energy; followed by a blood sugar crash leaving you lethargic and craving more sugar. When you eat a banana, you experience an increase in potassium (necessary for proper functioning of your muscles as well as your nerves), Vitamin C (needed for the absorption of iron), Vitamin B-6 (for new cell growth), Manganese (bone health), Fiber (helping you stay full longer), as well as energy in the form of carbohydrates.
Just the fact that you work at a healthy restaurant does not mean that you know ALL about health. When you spout off and say that sugar is sugar and your body responds the same way to a cookie that it does to a fruit smoothie is just ludicrous. Then, when someone who has made this their area of study for the past several years tries to enlighten you on the subject perhaps you should listen to them and not insist that you know what you're talking about.