> Actually carbs are necessary
This is NOT true. Carbs are ONE form of energy that the body can use for fuel. Fat is the other one.
> people with diabetes tried to live on a completely carb free diet - but you cannot do that for long.
I guess you're saying I don't exist?
For about 10 years, I haven't eaten carbs beyond the VERY rare cookie or two every other month and the insignificant trace amounts in above-ground leafy vegetables and the like. I'm not alone, there are lots of us who eat this way. Whole online communities, full of people who each have their own reasons. I did it for general health and fitness reasons, others do it to reverse their type 2 diabetes.
In the 1960s, a man named Angus Barbieri fasted for over a year under medical supervision and suffered no ill effects afterward. Unless you want to believe the whole thing is a hoax and he was secretly snarfing donuts on the sly, he is proof that humans don't NEED carbs.
The planet used to be dotted with cultures that eat animals and fish primarily or exclusively for hundreds to thousands of years. The Inuit, Mongolian nomads, tribes in the Amazon, etc. They mostly don't exist anymore. (But not because of their diet.)
It's not a big group, but there ARE modern people who live on a carnivore diet for years on end and don't appear to suffer any notable long-term effects. Generally these are either extreme keto/paleo adherents, bodybuilders, or those who are trying to manage a medical condition.