I don't mean to be disrespectful, but just like most LCHF proponents (or carbophobes ;) you are oversimplifying things and jumping to conclusions.
Fact is, we still aren't exactly sure about what we need to eat and in what proportions.
Thankfully most of us have an appetite that regulates our intake almost perfectly, so we do not need to worry much about what we eat, as long as we eat everything. However, in almost all cases where we try to cut out certain substances from our diets we find that bad things start happening, like sailors at sea.
You claim that BMI, a statistical tool, is bullshit. But what about the very weak (and in many cases irrelevant) statistical evidence for entirely turning what we've known about nutrition for thousands of years upside down?
We've been eating grains for 100k years, and grasses for 4M years. I'm not about to listen to a collection of kooks with an agenda to sell training and books for new age hippie diets.
Come back when you've tried this kind of diet for a few more decades, chances are you won't be there to tell about it.
I'm not saying you are wrong, what I'm saying is that you guys are being too vocal about something you still know nothing about.