I wonder this as well. Lustig seems to say that fruit is fine - the sugar in fruit is nature's way of getting you to eat the healthy fibre or some such - but I've yet to see a scientific explanation of why sugar is bad but sugar in fruit is OK. Sure there are good things in fruit, but if sugar is bad then surely you'd be better off getting those good things from other sources, like vegetables.
Sugar isn't 'bad', too much sugar is bad. Lustig says that the sugar in fruit is fine, and is the same sugar found elsewhere. It's fine in fruit because it's wrapped up in a fiber package, that prevents your body from absorbing most of it.
