Carbohydrates themselves are not necessarily "bad". They are a problem when...
1. they increase blood glucose levels above an ideal range. These are high GI foods like processed grains and sugars.
2. they come packaged with foods that have other "bad" things in them. This is a second argument against grains, gluten-contianing grains mostly.
3. the carbohydrate in question is fructose. Fructose intake above the moderate amount found in a few servings of fruit is hell on your liver.
The carbs of choice by many around here (sweet potatoes, squash, etc...) are free of all three of those issues.