Potatoes are not the devil incarnate.
In moderation, they are part of a healthy diet. What we do to them, from slathering on the butter to frying them, makes them bad as is having them as the bulk of your diet. You do need carbs in your diet, but not as many as most of us consume. I eat a LOWER carb diet and it works for me.
I find the glycemic index an invaluable tool. It tells you how easily carbs are converted to sugar by your body. The higher the index, the quicker your blood sugar will rise after and then crash, usually causing you to eat again to get your sugar level to rise again - i.e. the roller coaster effect. A lower index food will keep your sugar level on a more even keel.
I literally had to teach myself how to eat again. Portion control is a very big part of it. I also had to "unlearn" a lot of bad habits: eating when bored, getting off the sugar roller coaster, eating too many high calorie foods while out, etc. And I totally agree that exercise IS a must.