Good question, because a carb is not a carb is not a carb. A bowl of ice cream or a giant sugary drink is not a plant. Neither is white bread that's got 50 ingredients. So there are differences.
Lots of folks just think "Carbohydrate is bad" and take it no further. I really don't know what's in the mind of someone who drinks a sugar free diet soda. I don't know what they are trying to do.
Carbohydrates are generally bad, and are implicated more and more in all of the diseases and conditions of the Western way of eating. That something bad can be mitigated or made partly better does not change the fact that it's mostly bad. This gets to your "a carb is not a carb" comment. What differentiates different sources of carbohydrates, and makes some "healthier" than others, is just how easy it is for your body to absorb the actual carbohydrates. The easier it is, the less healthy the food. The only reason refined carbohydrates are called junk carbs and whole wheat is called healthy carbs is because of all the stuff in whole wheat that interferes with your body's absorption of its carbohydrate content. Fiber, on its own, is not healthy; it's just good to have around as a barrier between the carbs and your bloodstream. Why bother with the carbs in the first place?
Fruits and vegetables are different evolutionary strategies in practice. Fruits want to be plucked and eaten so their seeds can be spread around, which is why they taste so good and provide at least some vitamins (though no required nutrients that we can't get from meat). Vegetables don't get much out of being eaten, and since they can't run or fly away from predators, evolved a huge array of anti-nutrient toxins that render them basically inedible to the majority of animals. Most wild vegetables, to this day, are inedible to humans unless cooked, and much of the nutrients they contain is not absorbed at all because of the indigestible components. We have engineered certain species to be easier on our systems, but all this shows is that we never needed them to begin with, as these are without exception millennia younger than our digestive systems.
There is no actual need for any carbs at all in the human diet, which makes sense as we evolved during times when they would have been so scarce compared to meat that we couldn't justify spending the energy to find them. Our ancestors thrived in deserts, ice ages, and plains before learning about agriculture, and with occasional opportunistic exceptions favored meat for most or all of their nutritional needs. I'm not saying we should all eat like that today just because they did it back then, I'm just saying this is prima facie evidence that our bodies are well-adapted to life without any carbs at all. How numerous, energy-rich, and palatable do you imagine the local flora were before we learned how to breed plants that actually taste good and grow all year-round? Sure, our ancestors ate plants, but we're not talking kale salads with sweet corn, we're talking bland tubers from the bottom of a lake that they relied upon as an absolute last resort. And if they got lucky, some berries that weren't poisonous.
Meat, on the other hand, has been the same nutrient-dense, delicious, easily digestible energy source that it was a million years ago. It helped us grow big brains compared to the rest of our bodies, which in turn helped us devise better hunting strategies, and that feedback loop is really what made humans human.
There is a
growing community of people who, like me, eat nothing except for meat every day of their lives. Some have been at it for years, some for decades, and with almost no exceptions they report excellent health, great cholesterol numbers, more energy, and a complete lack of obesity. Gut disorders vanish (in my case this has been a miracle), inflammation doesn't happen anymore except when it's needed, bloating is a thing of the past, and every meal is just as satisfying as the last.
I'll again add the parting disclaimer that my purpose in mentioning all this is NOT to say that everybody should adopt this diet. I don't care what you eat if you are happy and healthy, and there is more than one way to achieve that balance. Rather, I am only trying to refute the claim made by others that MY diet cannot be healthy, because it is lacking in certain components necessary for my health and prosperity, namely plant matter. The assumption is that the burden of proof should be on me to show why we DON'T need to eat plants, when scientifically, there is no compelling evidence to justify that default position. Based on our evolutionary past and an emerging body of research, the onus is the other way around. If you want me to believe that I need carbohydrates for any reason, or that I should be consuming plants regularly, show me what I am missing and why I need it, and explain how so many people (both 100,000 years ago and today) are managing just fine if not better-than-average without them.