Observe this man:
The text reads: "This version of the posture requires considerable strength in the neck, shoulders, and back requiring years of practice to achieve. It should not be attempted without supervision."
Actually, it should not be attempted at all.
In this position, blood pools in the head (the head does not have valves within the veins for venous return to occur to force blood back towards the lungs for re-oxygenation).
Also, the cervical vertebrae are literally being compressed and crushed.
Furthermore, it does not take great strength in the arms, shoulders and back to do this 'position.' In fact, it takes no strength at all.
But it takes great strength to get out of it!
I have no real beef with Yoga. But I do take issue with people putting themselves into positions or performing certain exercises for the purposes of improving their health that actually cause them harm.
Hey I care! So sue me!