No, Ketosis is not the goal of fasting. Detoxing, rebalancing and healing the body are the the primary objectives of fasting. Ketosis is a by-product in that it happens and is to be expected when fasting.
I've never had a ketone problem and I've never come across anyone else having a problem with ketones. I mean, anyone who fasts or goes on a low/no carb diet will have ketones show up, but it has not been a problem for me and I have never heard of anyone else having a problem. But that does not mean there is not a first time for everything.
Understanding the role of ketones in the body and how they are triggered can help relieve some of your anxiety. You're juice fasting, so the lack of calories and low carbs consumed during fasting has dramatic effects on the body’s systems. Because of the lack of glucose consumed, the liver converts glycogen stores into glucose and energy. The brain and the central nervous system need direct glucose, so they must get it either from the breakdown of proteins or fatty acids. The body resists breaking down the proteins, so fatty acids, after being converted into ketones, become the primary source of energy. Ketosis is subdued by drinking plenty of fruit juices, which provide simple carbohydrates for energy and cellular functioning. So if you're overly concerned about the ketones, drink fruit juices everyday, in between your veggie juices. Experiment.
To help during times of fasting, these ketones automatically suppress the appetite. They are the broken-down products of fatty acids. When you fast, the body releases these ketones into the bloodstream - which helps tone down the misery of hunger pangs. As your body begins to metabolize fat stores, you may also notice that your breath takes on a sweet or fruity aroma. That's produced by acetone, one of the ketones produced when fat stores are burned. The symptom is harmless. Ketones in your body is a good sign you're burning stored fat.
However, if you have a rare condition where you are unable to process ketones (MCAD deficiency), you should not fast. Otherwise, in my unprofessional, yet somewhat experienced opinion, with juice fasting, there is less ketosis (as opposed to other types of fasting and dieting (Atkins, for example), and the simple carbohydrates in the juices are easily used for energy and cellular function.