1. Religious fundamentalists believe in supernatural beings. Low carb talibans believe you can get fat without a positive energy balance, if you eat carbs.
Similar to the anti-fat proponents 15-20 years ago, we now have one group of people blaming one particular macronutrient as the sole reason for why people are getting fatter.
2. Religious fundamentalists base their beliefs on faith, not empirical evidence. Low carb talibans believe that dietary fat is unimportant for the development of obesity; the most jaded lot believe that you can eat an unlimited amount of fat, without weight gain, as long as carbs are excluded from the diet.
The 'rationale' behind this claim, is that the body can’t store fat without insulin (it can). Carbs equals insulin, and that means ditching carbs must mean no fat storage (wrong). They conveniently ignore that
a) eating protein produce insulin
b) fat stores itself with tremendous efficiency without insulin, due to a nifty little thing called acylation-stimulating protein (ASP).