It is true that even fresh fruit juice contains a lost of Sugar which will raise your insulin levels and depress your immune system.
I do not understand why you have been juicing only fruits or why you seem to think that juicing refers only to fruits. Most juicing information recommends that you juice primarily vegetables, which, with a few exceptions, are much lower in carbs than fruits; you can combine them with fruits, although some sources don't recommend mixing fruits and vegetables. However many people enjoy, for instance, mixing a little apple juice with more bitter tasting vegetables when they juice in order to make the juice taste better.