1) Actual pressed juice is fine. The matter gets confused when people don't realize that a glass of actual orange juice is 6+ oranges worth of juice. You wouldn't eat a dozen oranges without thinking about the caloric intake. But you'd drink a few glasses of OJ because it's not as filling.

2) Thermodynamics... That said, a thousand calories of soda is half a day's worth of energy in sugar form. Your body uses sugar first when available, as a general rule of thumb. If you ate any fat that day, it will use the sugar, store the fat. More efficient than turning the sugar to fat, which we are bad at. (Humans aren't great at ketogenesis.)

3) Your body also understands sugar just as well. Blood glucose is an important bodily stat for good reason. Your body also uses protein and various trace elements in your diet, and it "understands" and "uses" all of them. Sugar is just more convenient to use than fat, so it uses that first and stores the fat. On ketosis, you just end up taking some of the stored (or dietary fat) and turning it to glucose in a hugely complicated process (think of it as "inefficiency in storage/packing/unpacking" the sugars into fats and back) and then using that to feed the ATP cycle to run the furnace. You don't run on fat. You store glucose as fat because high levels of glucose in the blood are bad. And then you store the fat outside the blood because that too, is poisonous in high amounts (see ketoacidosis). Your body is a fine-tuned machine that runs on pure glucose and happens to have a set of machinery that makes all animal/plant inputs (fats, sugars, protein, minerals, vitamins) into either A) machinery bits for maintenance or B) more glucose to burn.

4) Sugar (whether it is glucose, fructose, sucrose, lactose, maltose, w/e) is a functional way for a lot of things in nature to feed themselves, including us. Whether it is honey, the inside of an apple, or a grapevine, lots of things are full of easily digested sugars. Sugar, as much as you'd like to claim is "not necessary", is everywhere in nature, as it is a part of most living things.

5) Salt is bad, indeed. As a general notion, equilibrium should be attained in the body fairly easily. The bigger problem people don't think about is the K/Na ratio and such. As a general rule, salt is overused in our food. That one I agree with. No idea why you tacked on anything about sugar here.

6) Energy in, energy out. You're just a fancy (REALLY fancy) way of burning food slowly (given that you exhale some carbon in your food through CO2... and you used the O2 you breathed in to combust that food.) You happen to do useful work with the fact that you can invest a small amount of energy to gain a lot of it. It's a side effect. Locomotion and keeping the food-burning oven running and clean are the main reasons you use calories. The problem with the OJ glass at breakfast is detailed in 1) and has nothing to do with sugar and everything to do with the fact there's little finer and little satiation to orange juice so you drink far more calories than you'd ever eat from the actual fruit.

We prepare foods for easy consumption, but a lot of food is made to be filling as a way to self-restrict. Our more basal impulses ("eat until you're full because there may not be more food for a while") are woefully maladapted to our world.