Murder is a Common Law offence, so the idiots who come up with the rules are judges.Nope, it's the idiots who come up with the rules and regulations that are missing something. I think the idea of murder has to have some kind of 'cunning plan'! Spur of moment killings slot into manslaughter. Violence should be off the streets no matter whether there's a previous blueprint or not. Any death that is the result of a crime should not be treated leniently.
Briefly, the law that was followed from c18th was that murder required intention to kill or intention to cause grievous bodily harm. In modern times it has been called into question whether intent to cause GBH was sufficient to sustain a charge of murder. The law commission recommended a new law under which: first degree murder required an intent to kill, second degree murder required an intent to cause GBH, and lesser intents would be Manslaughter. The difference would be in sentencing: mandatory life for first degree, discretionary life for second degree, and lesser sentences for manslaughter. The recs were never enacted, but prosecutors nowadays are reluctant to bring a charge of murder, unless there was evidence of a clear intent to kill. They tend to charge with malicious wounding or similar offences.