Actions have consequences.
If you want to risk your own life, many people would say that that is your choice. If the risk fails, you pay the consequences.
If you want to risk other people's lives, that is not your choice to make. However, if the risk fails and you take an innocent person's life, it would be perverse to say that that's their problem and that you should not be punished more for killing someone than someone who drove dangerously and didn't kill anyone.
If you batter someone (what most people think assault means) and they die, that's manslaughter or murder. If not that's assault and battery or common assault (or GBH, ABH, or whatever). Same action, different offence and punishment for a different outcome.
The test for dangerous driving is effectively subjective insofar as it cannot be scientifically measured. Doris who never exceeds 25mph on her weekly shop will likely have a different opinion than Kev who drifts his car round roundabouts to try to impress schoolgirls.
If your driving is a causal factor in somebody's death, not so much subjectivity involved.