> Sugar is readily accessible fuel, that's why you crave it. Complex carbohydrates and starches are the problem, not sugar. If you get a crash that's because you need to eat regularly, just like all the other primates. Fasting is an emergency state, not a normal one.
If you get a 'crash', it's because your blood sugar level is too low. One way that this can happen is by eating refined (simple) carbs - aka sugars. The release of sugar into the blood-stream is fast, leading to a large release of insulin from the pancreas, which then drives the sugar in the blood stream into the cells, giving a consequent drop in blood sugar. Unless you then replenish the blood sugar you get a 'crash'. Far better is to eat in a way that doesn't give you that spike of blood sugar, so that the insulin response is less.
> Have you ever felt tired and out of whack after eating fruit?
No, not that I can think of specifically related to fruit.
> Have you seen the size of people on a fruitarian diet? (Spoiler, they loose a dangerous amount of weight).
Not sure what an anecdotal observation of people on a weird diet proves.
> You don't get fat by eating fruit
No-one said you did. And (spoiler) not all sugars are equal. Eating a piece of fruit is not the same as eating a piece of candy, just because they both contain (some wort of) sugar.
> you get fat by eating lots of pasta and bread.
(This is a weird and partly incorrect statement, but...) Who said this was about getting fat? There can be negative health effects from what someone eats, aside from weight gain.
> I challenge you to gain weight on a diet of steak and orange juice.
Not sure what this weird unbalanced diet would prove either?