Spectrum has defended its actions, saying the company is contracted to support people to make their own choices.
People with "diminished competence" retain the right to make informed decisions about their lives.
The son's adopted mother told the Herald he was a vulnerable person of limited intellectual capacity.
"It's very much like dealing with a very small child."
Though her son identified as gay, he had never had an actual relationship that she knew of.
He would strike up periodic friendships online but they usually ended quickly with him being "dropped and blocked on Facebook".
The mother said her son seemed to be "well received" by older men in their 50s and 60s.
His parents had fought hard to get their son the support he currently has. They feared he could be sexually abused if he'd travelled abroad to meet his new 55-year-old "boyfriend" Michael - or wound up unsupported on the streets if the court hadn't stepped in.
"We do think he could end up in some kind of sexual abuse. He really doesn't know. He's not an intelligent man."
The couple adopted their son from an orphanage, but were not told he was intellectually disabled.
The mother said her son had never had a proper job. He'd resided in the supported living facility for the past four years.
Their son met Michael online in about September last year and the pair's relationship quickly progressed to frequent phone calls and plans for their son to move to Florida to live with the much older man.
Alarmed at the proposal, the parents wrote to Michael informing him of their son's significant intellectual disability and asking him to "slow things down".
They also suggested Michael travel to New Zealand after the pandemic to meet with the family in person.
"We don't know you Michael. We are not capable of judging your character," they wrote.
"If things sour between you two what will happen then?"
Michael replied, saying their son was "an obligation that you weren't prepared for".
"I'm assuming from your letter that you gave up on [your son] many years ago."
Michael disputed their son's low IQ assessment, claiming he was an "intelligent young man" who would be safe with Michael, who assured the couple he was "a good person".
"You should know that [your son] is not happy with his life in New Zealand. He will find a way out. Hopefully he doesn't find the predator you guys have been manifesting."
Alarmed at the looming trip and their son's vulnerability, the couple asked Spectrum Care to intervene.
But they say Spectrum bosses were unable to help, claiming their son was an adult who had the right and necessary understanding to make his own decisions.
"We aren't saying we are not concerned about [your son] going to America, we are not saying we don't share exactly the same concerns that you have," a Spectrum manager wrote.
However Spectrum had developed "mitigation plans" to help their son access "personal networks" in America, the manager said, and the company did not support restricting his human rights.
The mother said Spectrum workers helped her son arrange his flights, drove him to the bank to withdraw money and even helped pack his bag in preparation for the trip.
"If our son wanted to free climb a sheer cliff ledge after watching Mission Impossible, would Spectrum Care help him buy climbing shoes and drive him to a ledge?"
At their wits' end, the couple then turned to Adult Guardianship Services Trust director Helen Peterson.
Despite Spectrum's position, Peterson felt the man was at risk. She applied to the Family Court for an emergency personal order on the parents' behalf preventing him from travelling overseas.
A lawyer representing their son was appointed by the court. She endorsed the emergency application, which was granted on November 27.
The parents say their son has now turned against them. He blames them for keeping him from the loving relationship he believes awaits him overseas.
"He refuses to speak to us. He thinks we're evil."
Peterson told the Herald the son had a reading age of 7 or 8, could not tell the time, or do basic maths, had a history of sexual assaults and limited understanding about money.
She said it was distressing that although Spectrum had clear evidence the son was a vulnerable man at extreme risk of emotional, physical, financial and sexual abuse, it was "unwilling to support the family, nor consent to a court order to safeguard him".
She said it was even more distressing that Spectrum was willing to let a client with a serious learning disability, behavioural concerns and limited money travel to a Covid-19 hotspot to live with a man he had never met.
"This is assuming he would even get to his destination, given the logistics involved, his disability, his finances, his IQ and his age."
The case highlighted a lack of legal protections for vulnerable adults "in need of safeguarding due to cognitive incapacity".
In a statement, Spectrum Care said staff expressed concerns to the son about his decision to travel but they were ignored.
The company then suggested the parents apply for welfare guardianship to prevent the son travelling, but say this was also declined.
"From that point on, our obligation was to support the individual in his decisions and we worked with him to ensure safeguards were in place for him while travelling."
Spectrum Care was contracted to support people to make their own choices, identify risks and help mitigate potential harm.
If a person had diminished competence, they retained the right to make informed choices and give informed consent, unless a court-ordered process was in place which legally transferred the decision making process to someone else, Spectrum said.
"No transfer of these powers to make decisions were in place during this time."
