Except for the fact that carbs are the only macronutrient that are not essential and can be completely synthesized by the body via gluconeogenesis. There are essential amino acids that need to be sourced via food (protein). There are essential fatty acids that need to be sourced via food (fat). There are no essential carbs.

From a practical standpoint you are correct; however, it is very difficult to have a zero carb diet, so I don't think this theory has been 100% tested. At least, this is the impression I got reading this opinion paper. (http://ajcn.nutrition.org/content/75/5/951.2.long) I think even most ketogenic specific diets aim for around 5% carbs.

Some other aspects of carbs seem to be not fully investigated, such as the effect of dietary fiber's role in nutrition. While not "essential" (http://jandonline.org/article/S2212-2672(15)01743-8/abstract) it seems to play a mostly positive role. (If only to prevent constipation...)

At this time, I'd think "fad" of any ketogenic diet advocate that has little vegetable consumption. But as the first link states, "most of the current low-carbohydrate, weight-reducing diets advocate the consumption of low-carbohydrate vegetables". "Eat more veggies" has been a mantra of dietary advice for a while. :)

No carbs is really hard if you exercise, or are an athlete. I stick to a low carb diet, but I can't imagine cycling/running 50+ miles a week in combination with weightlifting every other day, if I didn't have the energy from carbs. Chicken breasts and vegetables just aren't enough for me. (Carbs for me is usually oatmeal breakfast and protein bar)

Which is how we reclaim energy from Fat yes, but the biproducts of that process can lead to A) Gout B) Kidney stones C) Appendicitis and a number of other wonderful issues. Look at morbidity among various arctic cultures (Eskimos, Siberian Reindeer cultures) for more details.

Sure. But if you live even a little bit active lifestyle, you are going to have issues with this, as converting fat to energy is a much harder process.

You can try to counter the point by pointing out that there are ultra-marathoners who are keto. But my two counters against this are:

1) They generally still use some form of carbs during the race, i.e. sugar packets.

2) There is no world class sprinter / 5k / 10k / sprint biker / football player / soccer play that is keto.

So fine, you can make the argument that no carb is a better diet for an office potato with no exercise. But I would argue that bumping your carb intake up 25-40% and doing some exercise is going to lead to a much more healthy body and mind (many studies around on the benefits of exercise).

TLDR: The problem with office potatoes is being an office potato. You are better fixing it via exercise, vs trying to eat a weird diet that lets you stay skinny while an office potato.

Why avoid carbs?