Alcohol-affected violence is not new to Sydney streets — it started with colonisation.

However, patterns of such conduct, now fuelled also by drugs (especially amphetamines and steroids), do change.

After violent events that resulted in deaths, the O’Farrell government has been stirred to act.

One-punch assaults causing falls and brain damage often leading to death are an ongoing scourge in Sydney and elsewhere and usually result in manslaughter convictions and penalties.

Instigators of such violence may do it simply because they can, because they think they can get away with it and because they like to feel the power it gives them.

The fact they are intoxicated serves only to weaken such inhibition.

So the source of the problem rests with the nature of the individual attacker, and education and proper social conditioning probably need to be improved.

That is where most attention should be focused.

The pattern of attacks seems to be connected with the availability of alcohol and a concentration of liquor (and drug) outlets — thugs are drawn to the honey-pot of victims found in such hunting grounds.

In Premier O’Farrell’s plan, one wonders just what is sought to be achieved by increasing some criminal penalties; and there is no justification for introducing mandatory sentences of any size for some serious offences.

As former Chief Justice James Spigelman said in 1998: “The preservation of a broad sentencing discretion is central to the ability of the criminal courts to ensure justice is done in all the extraordinary variety of circumstances of individual offences and individual offenders.”

Governments are fond of tough-sounding announcements of more criminal penalties — they must believe such measures are effective, but they are not.

There is plenty of evidence increases in penalties do not produce corresponding deterrent effects and that mandatory minimum sentences do not deter offenders, but complicate and add to the expense of criminal proceedings and require courts to act unjustly.

The government proposes both of these courses for nine offences of violence (including sexual assault and assaulting police) “where drugs and alcohol are involved”.

Available maximum sentences would increase by two years and new mandatory minimum sentences of between two and five years would apply.

Where drugs and alcohol are involved in such assault offences, the last thing an offender thinks of is the penalty possible.

It is also proposed that self-induced intoxication by drugs or alcohol will “be removed” as a mitigating factor in sentencing, but it is not now a mitigating factor under sentencing legislation and courts do not excuse offenders just because they were drunk.

An increased maximum of 25 years (from two years) for the illegal supply and possession of steroids is probably unobjectionable, but is likely just to drive the market deeper underground.

There is also a proposal to introduce an offence of unlawful assault occasioning death with a 20-year maximum sentence.

There is no need for it; manslaughter is the appropriate offence in NSW and its maximum sentence is 25 years.

In 1883, in NSW, the Criminal Law Amendment Act was passed after public agitation, prescribing, for five categories of maximum sentences, corresponding mandatory minimum sentences.

When the law was implemented, injustices quickly became apparent and, after sustained public reaction, this time against the provisions, they were repealed in 1884, after less than one year and one month.

Is history to repeat itself?

Nicholas Cowdery AM QC is a former director of Public Prosecutions, and adjunct professor of law at Sydney University.