Mr Smith said he is glad a package of nine mandatory prison sentences proposed by the O'Farrell government to deal with drunken violence didn't pass parliament this year.

"Quite frankly, there was an upsurge in the number of people in prison... Why do you need tough sentencing when the crime rate is dropping?" he said.

The prominent Catholic exits politics at the March 2015 election, after being dumped from cabinet when Mike Baird became premier.

He had reluctantly toed the government's line to speak in favour of mandatory sentencing for nine violent offences involving alcohol in parliament. But speaking freely after the final week of parliament, Mr Smith now says only the "one punch law" for homicide was necessary.

"There was a crisis, certainly a crisis in public confidence. I did support mandatory sentencing for that particular offence," he said.

When he entered politics in 2007, he wanted to improve rehabilitation and move away from the law and order debate, which was "too much aimed at locking people up and throwing away the key".

Mr Smith said a surge in the prison population, to a record 11,000 in May, under his watch, might have been due to increased policing activity, but wasn't the result of increased crime.

His response to the push for tougher sentencing from the Daily Telegraph is "tell them to get stuffed".

"People think you are arrogant when you say, 'They don't know what they are talking about.' But they don't sit in court, sitting up on the bench. It is so difficult to make public policy on the law. You get a few people who realise their ratings will go up if they go tough. I don't think the hardline approach works."

Mr Smith said criminal law was fascinating, with some people prepared to forgive the worst things, while others sought vengeance through tougher laws.

"They think that's the way they will get some kind of personal healing, but they can't... the justice system is imperfect," he said.

The former president of Right to Life NSW, Mr Smith supported Zoe's Law and lashed out in parliament at its opponents when the bill lapsed.

He said he was entitled to stick his neck out as a Catholic politician and had been "abused for it".

Against a backdrop of 10 MPs stepping down from the Liberal Party amid corruption allegations, Mr Smith said following the 10 commandments would stop a politician stealing or bearing false witness.

"If someone is well formed in Christian teachings they should be an honest politician, which is what we want," he said.

"Once you become a minister and attorney general you have to be careful, because it is hard to separate government views on a law from your personal views. There may be issues you don't particularly like, but have to go ahead with."

Mr Smith said former Labor premier Kristina Keneally's public comments on many issues didn't represent mainstream Catholic teachings, and she hadn't voted according to Catholic beliefs on issues such as same-sex adoption.

He counted restricting sexual violence on R18+ rated computer games as a victory for his moral beliefs.