"A person in the wrong environment, with the wrong stimulus, in the wrong frame of mind - they can do unspeakable things - that is pretty terrifying," Cain told the Herald.
"Anybody is capable of doing something terrible if they feel like their back is completely against the wall, that there are no political options left. If the conditions of my life had been set up in a certain way, that could have been me."
He had read the now-banned March 15 manifesto.
"I had believed in watered-down versions of all that white nationalist stuff. I'd believed in 'Western values' or 'European values', the great replacement and Muslims invading our nations, that we needed to fight militarily if need be."
He had also watched a video of the now-banned livestream.
"It f***ed me up because I had in some shape or form participated in that."
His descent into the alt-right started in 2014, when he dropped out of community college and struggled with depression. He slept all day, spending countless hours on the internet while his "muscles atrophied".
One day, YouTube recommended him a self-help video by alt-right figure Stefan Molyneux, who was at the centre of a controversial visit to New Zealand in 2018 when Auckland Mayor Phil Goff banned him and far-right activist Lauren Southern from speaking at Auckland Council venues.
Inspired by the self-help video, Cain dived deeper into Molyneux's catalogue, which included videos on his white supremacist views.
Over five years, Cain watched thousands of videos a year of a similar political persuasion.
"I was aware that I was becoming right-wing. I was a liberal progressive in high school but I thought I was now hearing the truth. Everybody else was wrong.
"I became more and more extreme as time went on. At the very end of it, I was what they call a civic nationalist. I would not have called myself a white nationalist. It's kind of like fascist-light."
Cain never became anything close to a militant white supremacist, but he remembers the night of Donald Trump's presidential victory in 2016 as an "ecstatic" emotional moment, and says he would have been prepared to throw himself into a street brawl to protect "American values".
The use of online platforms to spread hate and radicalise users has come under intense scrutiny, especially since March 15, with YouTube a particular focus because of the way it tries to keep users on the platform for longer.
Centre for Humane Technology co-founder Tristan Harris, who used to be a design ethicist at Google, which owns YouTube, has described YouTube recommendations as tilting users towards "crazy" content.
"A teen girl watching a dieting video, they recommend anorexia videos because they're more extreme. If you start someone on a 9/11 news video, they recommend 9/11 conspiracy theories."
YouTube officials have denied that its algorithm steers users towards radical content, adding that it continues to work towards protecting users from misinformation and extreme content.
Cain is reluctant to solely blame YouTube and accepts some personal responsibility.
"Real brainwashing doesn't exist. People get influenced and then they make their own decisions, but I was so stuck in a filter bubble, cut off from other information."
The same platform that enticed him towards the alt-right also helped rescued him. In 2018 he watched a video debate between Lauren Southern and Steven Bonnell, a liberal YouTuber known as Destiny, expecting to cheer on Southern.
But he found himself sympathising with Bonnell.
"That was an epiphany moment. But that didn't stop me from being right-wing. That was a long process that took a lot of reading and watching videos and having conversations with people.
"I was confused. It wasn't until later that I realised all the stuff I had believed was basically Nazi-conspiracy theories and white nationalist arguments. That was really shocking to me."
Cain had already decided to help people stuck in an alt-right filter bubble, but March 15 gave him renewed impetus. About a week after the attack, he published a YouTube video about his own experience.
"It was probably cathartic to just come clean, kind of peeling back the curtain on this whole process, and maybe someone could watch it and see themselves in it."
His channel, Faraday Speaks, a homage to the 19th-century scientist Michael Faraday, now has 21,700 subscribers, and Cain continues to use it to counter the alt-right.
He also set up a Discord Server chat room to stir constructive conversation for people of all political persuasions.
"We basically put people on the far right with people on the far left and people on the centre together, and we moderate their conversations.
"If they spend time talking to each other and building relationships, it'll be harder for them to dehumanise each other. And then hopefully that will start to moderate some of their political views.
"All tribal groups dehumanise the people that they don't like or are afraid of."
Cain will visit Al Noor Mosque on Sunday, where he will meet victims and their families.
He also hopes to produce video content to humanise the tragedy.
"The goal is to pay tribute to the victims, and hopefully to show the human side to some of the far right people that watch my channel.
"It will make it more real for me, not just something that happened on the other side of the world, and it will hopefully make it more real for them."
Where to get help:
• Lifeline: 0800 543 354 (available 24/7)
• Whats Up?: 0800 942 8787 (1pm to 11pm)
• Depression helpline: 0800 111 757 (available 24/7)
• Youthline: 0800 376 633
• Kidsline: 0800 543 754 (available 24/7)
If it is an emergency and you feel like you or someone else is at risk, call 111.
