Evidence shows that Bill Cosby has an uncontrollable urge to violate young women and would likely reoffend if given the chance, a Pennsylvania state board psychologist says.

The 81-year-old comedian’s sentencing hearing has opened with a debate over whether he should be declared a “sexually violent predator”, which would subject him to mandatory lifetime counselling and community notification of his whereabouts.

Cosby, who faces up to 30 years in prison for drugging and molesting a Temple University women’s basketball administrator in 2004, fought the prosecution’s effort to classify him as a predator under state law.

Pennsylvania state board psychologist Kristen Dudley testified that Cosby has an uncontrollable urge to violate young women and would probably commit another offence if given the chance.

Ms Dudley added that Cosby’s assault of Andrea Constand fits a long pattern of predatory behaviour by the former Cosby Show star.

Cosby often befriended women, then betrayed their trust by sedating them with drugs or alcohol and violating them for the “sole purpose of his sexual gratification”, Ms Dudley testified.

Trying to avoid the predator designation for their client, Cosby’s lawyers argued that the state law itself is unconstitutional.

However prosecutors told Judge Steven O’Neill the law is necessary for public safety, and the judge allowed the hearing on Cosby’s status to proceed.

The defence contended that Cosby is unlikely to commit another crime because of his advanced age and health – he is legally blind and uses a cane – and because there have been no new complaints to authorities since Ms Constand came forward in 2005.

The legal wrangling came at the start of a hearing that will determine how the comedian, once known as “America’s Dad”, will be punished for knocking Ms Constand out with pills and assaulting her at his suburban Philadelphia home more than 14 years ago.

Cosby was the first celebrity to go to trial in the #MeToo era and could be the first to go to prison – perhaps for the rest of his days – after being convicted in April.

Cosby, looking grim, walked into the courthouse on the arm of his longtime spokesman as protesters shouted at him. Ms Constand arrived a short time later.

At the end of a hearing that could last two days, the judge could sentence Cosby to as much as 30 years in prison or send him home on probation.

The state guidelines for someone like Cosby, with no prior convictions, call for about one to four years behind bars.

“Obviously, the allegations are serious, and, except for his age and poor health, would normally warrant some jail time,” said Samuel Stretton, a veteran defence lawyer not connected to the case.

In the years since Ms Constand first went to police in 2005, more than 60 women have accused Cosby of sexual misconduct, though none of those claims have led to criminal charges.

At least two of those women, Lise-Lotte Lublin and former model Janice Dickinson, were among those in the courtroom on Monday.