Pete, 57, who lives in Westport, Co Mayo, joined the Church of Scientology in England in 1986.
Over two decades he devoted himself entirely to its teachings, recruiting others and even sold his house to fund his drawn-out training.
But, over time, he eventually realised the whole thing was a "con", and now he's committed to getting this message across.
Pete, who organised a conference of ex-Scientologists in Dublin last weekend, said: "I would have given my life for Scientology.
"I did all I could on a daily basis to spread the message to others, I regret that, but I don't have any anger.
"I had a penny-dropping moment four years ago but I had been questioning my beliefs for 14 years before that. I realised I'd been duped and that everything I once believed was rubbish.
"I burned all my Scientology books on a bonfire and now campaign against this terrible con. I won't give up until everyone in the church is out."
English-born Pete got "roped" into Scientology in Sunderland while struggling for cash in the recession-hit late Eighties.
He was told that by joining he would earn around £200 a week. And he yearned for the fulfilment and promises of becoming a better person.
Pete told: "I was attracted not only by the idea of a religion that would make my life better and also the money. In my three years working in Sunderland I don't think I earned £200 the whole time, but I wasn't doing much else so I signed up.
"I proved very good at getting new members and selling courses so eventually I was given my own mission in Cumbria.
"Around 1994 my figures had plummeted and I left to live in Ireland but still considered myself a Scientologist.
"It was a terrible experience. At the time I thought it was wonderful but now I feel very differently.
"I sold my house to keep myself going during the lengthy Scientology training.
"Eventually I left the church in 2008 and I began protesting and haven't stopped. We organised this conference in Dublin to expose the abuses of Scientology. It is a racket and a con and it harms people."
There is no official figure for the number of Scientologists in Ireland but members of the church, founded in Los Angeles in 1954 by L Ron Hubbard, have claimed there are up to 500.
Pete reckons the figure is a more modest 30 or 40, but he's adamant even that small following is potentially dangerous.
He said: "It has been operating in Dublin for 20 years, a lot of people visit it, but a lot of people run out for one reason or another.
"What they do is get people in to do a personality test. Then they pick on an aspect of it and try to appeal to the person. A lot of what they say does make sense, so people begin to think, 'This is OK, they get me.' But they don't realise they are preying on their vulnerabilities.
"Another trick is sending around 'Say No To Drugs' leaflets, the message is of course good, but then the person gets in touch with Scientologists without even realising it and they get sucked in.
"It's a gradual process, it doesn't happen overnight, but the members are very dedicated and very well-trained and they genuinely believe they have supreme intelligence and they have it right while the rest of the world is just stupid.
"It's done by degrees, someone will say, 'Just read this book and see what you think,' then you might agree with a couple of small sections and they are focused on.
"Scientology is very broad and it's very clever and that's why people don't even realise they are getting pulled into it."
At last weekend's conference in Dublin members of the modern activist group Anonymous — wearing Guy Fawkes masks — stood among the 300-strong audience.
They are in their 20s or 30s and came from Ireland, the UK, France, Germany and the US.
One said: "Our opposition to Scientology started when the church tried to remove a video of Tom Cruise being interviewed about his faith from the web in 2008.
"We are against not only internet censorship but the abuses of the Church of Scientology. They should fear us."
The actor's devotion to Scientology hit the headlines again last week when it emerged as one of the leading causes behind his split with wife Katie Holmes.
As far as Pete is concerned brave Katie had no choice but to run from Cruise and save their daughter Suri, six.
He said: "She's such a brave girl. He's a very rich and powerful man — to take him on like that shows how desperate she was I think.
"I really admire her.
"Ultimately she has saved her life and her daughter's life. I just hope she has people around her to help her now, but I have huge respect for what she's done."