So you don't think a murderer, particularly a one time murderer who you're sure will never murder again, should face any punishment?
Let's frame it this way: the dad in the video, hes done "assaulting" the guy on the bicycle. Why should he go to prison? The threat is neutralized, hes not going to keep attacking him...
The guy on the bicycle, how do you ensure he won't continue to be negligent without the lesson he was taught in the video? Maybe he should go in front of a jury and have his legs broken so he can't ride bicycles anymore? How would you handle that? Not punishment, right, so how do you teach someone that negligence is dangerous to others? I'm sure someone has told him somewhere that fact, obviously he didn't internalize it.