The Government's revised "three strikes" bill is estimated to cover more than five times as many criminals as the original legislation, significantly widening it from the original target of the "worst of the worst" offenders.
The issue was highlighted in a Maxim Institute-sponsored lecture at Victoria University in Wellington by Auckland University professor Warren Brookbanks and law lecturer Richard Ekins.
The Sentencing and Parole Reform Bill, now before Parliament, would set up a warning and sentencing system for anyone convicted for one of 40 qualifying offences deemed to be serious violent or sexual crimes.
Strike one would be a normal sentence and a warning; strike two would be a sentence without parole; strike three would be the maximum sentence for that offence, without parole.
The original bill held that a conviction counted as a strike for a violent offence where the sentence was five years or more.
The initial proposal called for an extra 132 prison beds in the next 50 years; the new one is estimated to require 725 beds.
Professor Brookbanks said that "qualifying offences" was a much lower test, as it applied to convictions for certain offences regardless of how serious or trivial they were.
"The shift from qualifying sentence to qualifying conviction radically widens the scope, bringing far more offenders into the scheme," he said.
"Every instance of a qualifying offence [on strike three] will be treated as if it were of equal seriousness.
"The significance of this shift in scope is that the regime is not in truth targeted on the worst of the worst; the regime is much broader than that."
Professor Brookbanks later told the Herald that judges already had the necessary tools to properly sentence repeat offenders.
"There is at this stage no need to radically change the sentencing options that are available, but rather make more effective use of them."
He said that with no incentive to plead guilty to a strike-three charge, there would be more trials and appeals, which would be more stressful for victims and see court costs rise - a point raised by Labour critics.
Dr Ekins said the bill could see much harsher sentences for the same offence on strike three than on strike two, or see the same punishment for the same offence despite radically different seriousness.
Act MP David Garrett, who drafted the original bill, said he was comfortable with the changes and did not think that it would now include less serious cases.
"There is considerable prosecutorial discretion regarding what charge is brought - particularly at stage three - and I am confident only the most serious offenders will face the 'three strikes' regime.
"If anything, given the serious consequences of a third strike conviction, we believe it is just as likely that prosecutors will err on the side of lenience rather than 'overcharging' in the particular circumstances of any offence."
Mr Garrett said that appeals against strike-three convictions would not normally require the victims to give evidence again.
DISPROPORTIONATE SENTENCES UNDER 'THREE STRIKES'
Strike-three indecent assault (a drunken grope) gets 7 years.
A rape (strike one or two) with a guilty plea and no parole could get much less.
Strike-three unplanned street robbery with no violence gets 10 years.
Strike-three violent planned home or business invasion with no guilty plea and no remorse would be treated the same.
Strike-three street robbery with two persons (therefore aggravated) with no violence or planning gets 14 years.
The same offence, at strike one, would get 18 months to three years.