Earlier quoted context omitted.
Calories in/out is true. As in it is an accurate statement. The problem is that common examinations of diet focus on this math rather than what motivates humans to eat. It is like saying 'the problem with traffic is too many cars.' It is an axiom that does nothing to examine the causes. Admonishing everyone to 'drive less' will do very little unless several other systems are changed.
Its one thing to tell someone to "drive less" when they have to go to work and don't have the capital/opportunity to move closer or change jobs. Eating less is entirely a personal willpower issue.
The problem is if we could just increase will power for everyone, we'd cause more problems than we'd solve. Too much "will power" means literally insane people. You'll have people exercising until they die of exhaustion/stroke/etc. You'll generate anorexics. You have psychopaths since willpower overwhelms every other consideration. People pursuing self-destructive dead ends all over the place because they no longer listen to their bodies, their peers, or just plain common sense to STOP.
We cannot just increase will power. The problem is with the other side: the body thinks it's starving, so is triggering extremely loud survival instincts that overwhelm will power. We don't want to make will power so great that it always overcomes survival instincts (like the need for sleep, pain in a tooth or a sliver, etc... all these are things we want people to still respond to so they don't kill themselves), we want to tamp down this false survival instinct of hunger to that of a normal person.