Joe Rogan complained about the rule during the Kampmann-Sanchez fight, but the time has come to end this ridiculous rule. I believe it was the first or second round, Diego was bent over at the waist with Kampmann above him and repeatedly puts his hand down then pulls his hand up to avoid knees to the head. Obviously, this scenario is one of the worst cases of how the rule affects fights. Kampmann was in a clearly dominant position and knees were clearly what he wanted to use, but Diego simply used the rules to his favor to limit the damage Kampmann could do and gain a few seconds of recovery.
The second scenario I despise, is when a fighter "A" shoots in, gets stuffed and instead of paying for his missed shot, he simply turtles up, hands over his ears with his head tucked. His opponent "B" who in this scenario has no desire to go to the ground, has the option of throwing punches to the side of the head which are mostly blocked by the hands, or punches to the body. What usually happens is fighter "B" simply backs up, referee steps in and fighter "A" is allowed to stand up, and the game is repeated. With blows to the back of the head not allowed and the sides of the head covered, fighter "A" has very little to lose by repeatedly shooting against "B" no matter how many times he gets stuffed. If knees were in play while on the ground, I promise you fighter "A" would take much more calculated shots or get to his feet as soon as his shot was stuffed.
Strikers have to take calculated risks when they fight grapplers, i.e. using kicks sparingly and staying at distance. Allowing grapplers an "out" when fighting strikers has got to end.
I know why the rule is in effect, the thought of knees raining down on a semi-unconscious fighter isn't gonna win MMA any fans with the mainstream sports crowd. But did Diego's "motorcycle accident" face after that fight really do us any favors? This sport is always gonna have it's detractors, making rules with "fighter safety" as the excuse is ridiculous. MMA is not a "safe" sport.