Should the laws on murder be altered?

A piece in the Guardian today seemed intriguing. There have been calls from some barristers and solictors to alter the laws pertaining to murder.

Currently, the definition of murder in England & Wales is the killing of a human being or intention to commit Grevious Bodily Harm under the Queen's Peace. The actus reus (,i.e. the 'guilty act') for murder is homicide whilst the mens rea (,i.e. the guilty mind) is malice aforethought express or implied. The contention is that the existing legislation doesn't account for certain kinds of homicide, such as mercy killings and the 'battered wives syndrome'. An instance of mercy killing would still be charged as murder, whilst battered wives could use the defence of provocation (there are four defences one can use against a murder charge. These are provocation, suicide pact, diminished responsiblity and infanticide. Pleading one of these defences would lead to a charge of voluntary manslaughter).

Some lawyers are advocating that degrees of murder should be instituted (as used in the United States), which would account for the anomalies of the differing kinds of homicide.

Of course, I'd argue that it's the state's role to protect rights to the person (and property). I'm no expert in law, but I feel the current system would be acceptable in a libertarian society. If there is no genuine or conscious intent to kill, then the charge should be dropped to manslaughter either voluntary or involuntary.