The main problem is it just doesn't work. Very few people successfully starve themselves thin, and even fewer maintain healthy weight that way.
Those who do have a healthy weight rarely count calories.
The technical problem with calories-in calories-out, calorie restriction, calorie counting and exercise as weight loss strategies is that they reverse causality.
Instead of fixing your diet (less toxins) and quitting drugs in order to drive your appetite down and energy up, you try to reverse causality and use sheer willpower to starve or exercise yourself thin. So what happens? You get really hungry and really tired, and your body actually burns less calories (perhaps permanently).
When you see a really obese person, instead of seeing a lazy glutton (which they might be) you should see someone who is *starving*. Their body and brain are screaming at them to eat more and move less, because (thanks to diet and/or drugs) they can't access all that energy.