They further argue the bill goes against the principle of rehabilitating young people.
Testimony given Thursday at a justice committee hearing centred on the case of Ashley Smith, a mentally ill 19-year-old from New Brunswick who was originally incarcerated for minor crimes and committed suicide in a prison cell in 2007.
Bernard Richard, New Brunswick's child and youth advocate, who wrote a report on Smith's death, told the committee teens who suffer from mental illnesses are especially vulnerable while incarcerated and often do not get the services they require while in prison.
"Ashley cried out for help and she became progressively worse while in contact with the system," said Richard. "There are thousands of young Canadians out there suffering from mental illness, from behaviour disorders, from addictions, who come in contact with the criminal justice system. They should be diverted, directed to treatment - not incarceration. Inevitably, incarceration makes their conditions worse."
Smith was originally jailed as a youth in New Brunswick and eventually moved to the adult system, until her death at Grand Valley Institution for Women in Kitchener, Ont.
Richard told the committee how Smith's behaviour worsened to the point that she spent more than two-thirds of her time in prison in segregation for at least 23 hours a day.
She had 501 institutional charges and 70 criminal charges, with more than half laid at provincial jails, and 168 incidents of self-harm.
"The question should be, does our criminal justice system provide mental-health treatment for youths like Ashley Smith? The answer is a glaring no," Richard said after the meeting.
The federal government's bill - also called Sebastien's Law in memory of Quebec teenager Sebastien Lacasse, who was killed by a 17-year-old - proposes several changes to the YCJA, most notably making "protection of society" a primary goal of the legislation.
It would simplify the rules to keep "violent and repeat young offenders" in pre-trial detention when necessary, require the Crown to seek adult sentences for some serious crimes, such as murder and aggravated assault, enable courts to impose "more appropriate sentences" on violent and repeat offenders and would give judges discretion to publish the names of young offenders convicted of violent offences.
"We recognize that it is much easier to rehabilitate a young person than an adult. Therefore none of our proposals would change the importance of rehabilitating young offenders. Sebastien's Law would provide additional tools for the courts when dealing with violent and repeat young offenders who threaten public safety,"said Pamela Stephens, a spokeswoman for Justice Minister Rob Nicholson.
The bill would also add "deterrence and denunciation" to the sentencing principles. Some critics say those provisions are both ineffective and would take the focus off rehabilitation.