When one studies the Art of Natural Dressage, it becomes totally apparant by itself why one does not need a bit, even more so, it would get in the way.
As we do not strive for obedience but for self expression, communication and health.
In other words, if that is Mr. Karls opinion, well than it is. As far as I am concerned there is no scientific proof of this. The contrary seems to be coming out of scienticif research.
But anyway, what Mr. Karl thinks about bits or no bit is not of our (my) concern nor is it relevant to this forum.
What is relevant to this forum is when anyone studies Mr. Karl and finds anything he or she can use in the lines of AND philosophy.
Every teacher has something that an other can use, so I think.
When I was teaching in Capetown, I taught a wonderful dressage instructor who studies Mr. Karl... she rode all her horses bitless
I myself never studied him so I can not tell you anything about his training.
I studied Antoine De Pluvinel mostly. He used bits and spurs, preparing horses for war.
As I prepare not for war but for health and self expression, I can leave the bits, the spurs and the obedience out and still have magnificent training knowledge at my disposal which I use on a daily basis, showing the world that healthy dressage and natural collection is within everyone's grasp when the horse becomes the initiator of the dressage. not the human.
As Romy said, the world wide web provides massive spots to argue about bits and views of training.
Here we simply study The art of Natural dressage and keep ourselves to what our horses tell us to do.