Your body does need carbs, your body needs fat, your body needs calories, etc. The key is to balance everything. Eat GOOD carbs, eat GOOD fats, etc. You need these different things to stay healthy. Lean meats, whole grains, veggies, and water, water, water.
I have tried EVERY diet on the face of the earth. One thing about the Atkins/South Beach diet (and other such diets)is if you get on it, there is NO cheating. If ya slip up, you've completely thrown off the whole thing. Unlike just balancing everything, if you slip up then you just go back and balance again. But these diets are designed to "train" your body to burn fat differently than your body was designed to do. Throw in a burger (with the bread) and it throws your body out of the cycle that the diet intented to get your body into. It's not like the typical, "Oops, I had a few too many calories". So if you don't plan on sticking to it perfectly, it's not the diet for you.
The best thing that I have personally found is to make sure you get lots of fiber, low fat intake, eat good carbs (whole grains), veggies and water, water, water. This incorporates everything your body needs to function properly.