Legal cut or chip blocks versus illegal chop blocks. All of them entail 300 pound offensive linemen aiming at defender's knees. It is sort of like saying it is okay to stab someone with a knife in the chest but not okay to stab them in the back. Casey Hampton was targeted again. The practice should be deemed illegal if they are concerned about player safety.
This is a video showing young pups how to properly "cut" block. It emphasizes hitting the thighs just above the knee.
The NFL is permitting offesnive lineman to engage a defender then have a second lineman cut below the defender's waist aslong as they are lined up next to each other. In some cases, a tackle has literally dived at the defender's knees but no flag is thrown because they were lined up next to the other offensive lineman.
This is what happens in the college game with an illegal chop block with a defensive lineman engaged with one offensive lineman then taking out at the knee by a second.
Now just imaagine 300 pound offensive linemen being who now have the greenlight to dive after a defender's knees while engaged with another offensive lineman. If the NFL really cares about they will put a halt to this practice immediately and not wait for more defenders knees getting blown out.
Yeah, it will make it easier for defenders to defend - but defense is an integral part of the game too.