I didn't watch the video and can't right now.
Cut blocking - an offensive lineman diving/rolling at a defender's legs. This is perfectly legal and I don't get why it would be considered any more dangerous than other football activities. You don't dive headfirst at the guy's legs, your sorta use your body like a log to take out their legs. If done with poor technique, it could be dangerous, but nowhere near as dangerous as poor tackling (i.e. with your face down, neck exposed).
Chop blocking - when one offensive player has engaged a defensive player up high and a second offensive player goes for the legs. This is completely illegal and can be dangerous because you could be restricting the natural movement of the offensive player. Holding someone in place while someone else dives at his knees is totally different than diving at someone's knees who can move freely.
Defenders, of course, should be taught to look out for cut blocking. If you read it before they get to your legs, you can easily skip over the blocker and get a free hit on a QB/runner, which, of course, could also be dangerous is not coached properly, etc.
The point is cut blocking =! chop blocking. Two completely different things. One is legal, one is not.