It is the Crown's case that instead of providing a safe and secure environment for the boys in his care, Opetaia exploited them for his own sexual gratification.
His defence lawyers said the claims were fabricated and complainants invented them in the hope of being compensated for being abused in state care.
Over a five-year period in the early to mid-2000s, Opetaia ran an Auckland home for Child, Youth and Family. During that time, more than 150 boys ended up in his care.
Yesterday, the jury was told that in 2018 Opetaia pleaded guilty to sexually violating a 14-year-old boy in 2014. This conviction prompted a wider police investigation.
Defence lawyer Anouska Bloem said the allegations in this trial arose while her client was serving jail time for that conviction.
She said this made Opetaia an easy target for the allegations.
"That is why we say Mr Opetaia was low-hanging fruit - ripe for the picking, right for the targeting and making a false complaint. He had done wrong, he had admitted his guilt and he was in prison. What better man to accuse falsely - who would believe Mr Opetaia now?"
Giving evidence in his defence, Opetaia recounted his troubled childhood.
He said his grandparents were abusive and he spent time living on the streets but he was an avid boxer and started his own club.
He did not intend to start a home but troubled youngsters gravitated towards the boxing club.
"So I sort of realised that if you've got problems, come to the boxing club. That's pretty much what it was - a magnet to people who have problems. As long as those who wanted to get into the training side of things."
He said the boys were not allowed to come to his flat freely because he worried what they would do.
"I'm dealing with little thieves, if you like. These guys are little criminals, you know, that's what they were. Youth-justice, at-risk, high-risk youth. I didn't want to be ripped off by them, robbed if you like."
Opetaia said he never physically disciplined the boys but he did raise his voice and swear at them to get his message across.
He felt he could make a difference to the boys' lives, given his own troubled background.
"Give these guys a better chance than what I had or what they were used to. I had feedback from them about other places and it wasn't always good."
Among the boys in his care was Liam Ashley, a teenager who was murdered in the back of a prison van in 2006. Opetaia got emotional speaking about Ashley, and broke down in tears at one point.
He said Ashley's death - and the death of his own brother - led to a nervous breakdown and he stopped his caregiving role in late 2006.
He admitted to smoking cannabis, but denied ever offering the boys drugs.
The trial before Justice Gault and a jury of six men and six women continues.
- RNZ
