The LNP has introduced a private member's bill that includes a minimum mandatory sentence of 15 years for a person who has sexually assaulted a child, leading to the child's death, or failed to provide the necessities of life. Shadow Attorney-General David Janetzki insists the opposition's bill is targeted towards people who deliberately act violently towards or neglect a child and people involved in an accidental death would not be caught up. However, the bill has raised the wider question of the unintended consequences of mandatory sentencing. Retired judge John Robertson, the chair of the Queensland Sentencing Advisory Council, said it was actually mandatory sentencing that led to injustice. "It leads to injustice because its fundamental premise is that each offender and each offence is exactly the same," he said.

"You have the case of a young woman living in poverty, a single mother, who puts her six-month-old baby in the bath and goes out to have a cigarette on the verandah and the baby drowns. "[Then there's the case] where it's a stepfather, the violence against a very young child, often a baby, is protracted. It involves threats towards the mother not to seek medical attention. It involves the most appalling cruelty. "In the mandatory sentencing space, both those people would get the same outcome." Mandatory sentencing was "superficially appealing", "because it sounds as though you're really 'cracking down on crime'". "People think judicial discretion is some sort of trick ... it gives [judges] the opportunity to do whatever they like," he said.

"But in real life it's not like that. We're quite constrained by the law, firstly by the Penalties and Sentences Act and then the case law. "It's not like you can jump in and have a free kick." The former judge said mandatory sentencing would also make Queensland's overflowing prisons, already at 125 per cent capacity, even more crowded. It would affect marginalised and vulnerable members of the community more, Judge Robertson said, such as homeless people, young people, drug-addicted people, Indigenous people and people with a mental illness. Aboriginal and Torres Strait Islander prisoners already account for about one in three people in jail, despite making up less than 5 per cent of Queensland's adult population.

"It's a really complex, multi-faceted problem and the difficulty is, it's really easy just to say, well we're going to increase the maximum penalty or we're going to introduce mandatory sentencing - that's really easy," Mr Robertson said. "It's much more difficult to address homelessness, so really put a lot of money into public housing, and to address the relationship between mental illness and criminal behaviour." It is a position that is supported by Queensland Law Society president Bill Potts. "Mandatory sentences often cause injustice," he said. "What we are concerned about in this is where you put a straitjacket on the discretion of the court to take into account all of the circumstances, then injustices may occur."

Mr Potts said he did not want to express sympathy for people charged over the death of a child. "They would shock any reasonable person but there is a significant difference between offences which amount to a failure of humanity all the way through to people who are, for example, cold-blooded murderers for profit," he said. "If you equate them exactly the same then you are doing an injustice for victims and the perpetrators as a whole." Mr Potts said mandatory sentences could also lead to defendants choosing to go to trial rather than pleading guilty, increasing the workload of courts and affecting witnesses who must give evidence. "If you have a mandatory minimum, there's no incentive (such as a reduced sentence) for people to enter a plea at an early stage or cooperate with authorities," he said.