The portion where you talk about how knee injuries stay with people, is undoubtedly true. Which, along with the points made by +Locrian Phyrigian
, is why I agree this kick will and should be made illegal. I also now after some quick thought see that this of course is probably why other combat sports have banned the technique or never allowed it in the first place. The only flaw in your stance is in regards to brain damage. If one is to be sound and reasonable it is not wise to base something as complex as brain damage off the experience of one or even ten fighters. Im not trying to defend brain damage or sports that cause them. What I am saying is its going to take a while for the science and the politics to meet which of course is usually about profit and accountability. No corporation or institution wants to be held responsible for changing the habits and making the repairs caused by these problems. Fortunately though with NFL players retiring early(one guy just did a short stint and dropped a huge contract because of fear of brain damage), scientific evidence over time and even life long announcers admitting that they will and have never let their kids play the sport....these things are going to make it easier for newer sports to adopt safer rules and equipment. in short the cat is out the bag because decades have passed and all the evidence is accumulating.
I was watching Greg Jackson talk in an interview in a documentary and even he was saying that Jones has techniques that will be banned. it was an older interview so maybe he feels differently now. I also overheard Rogan also saying that he didn't feel the kick should be made illegal because a leg lock also hyper extends the knee like this kick. Doesnt mean he is correct and it doesnt mean he still feels that way. I just always find the varied opinions of the people closest to the octagon very telling of how faulty and subjective some of the rules can be. Which is normal and especially in such a young sport. anyway sorry for the ramble, Ive been watching a lot of bouts lately. im about to watch Jones vs Bader...which i have never seen, like right now. gotta love the interwebs