It is right that judges sentence criminals more harshly if they do not acknowledge the seriousness of their crime and fail to show remorse. This is because if they do not understand the gravity of their crime it suggests that they will need more time to be properly rehabilitated in the prison system.
For starters, a person has no justifiable reason to be driving that fast in the first place. Secondly, if the driver doesn't think that what he did was a serious incident, then I certainly believe the punishment should be stiffer. Messing around like that endangers other people's lives, and shouldn't happen.
Criminal sentencing should not be harsher if the criminal does not understand the gravity of the situation. People are punished for the crime they have committed and are not required to understand the socio-cultural or personal implications of the crime they have committed. Plus, how would this be implemented? Would everyone have to take some sort of test to determine if they respect the gravity of their situation and crime?
If the sentencing is determined by how seriously the defendant takes it then people can just fake it and get off with easier sentences. The only thing that should matter in the sentencing is the events that took place. Once again we are letting emotions enter one of the only fields that they are not supposed to enter. Law is supposed to be about fact and proving the truth but this says, say sorry and you get off easy and if you dont say sorry I will punish you brutally. How about we focus on the statutes that he broke and the damage that he caused?
If someone lost control of the car and hit a pedestrian, then I think a lenient sentence is okay. In all other cases, it doesn't matter if the perpetrator doesn't fully understand what he did, he should still be punished in accordance to his crime. I do think there should be exceptions to this though, for instance for disabled people.