The 'Grease!' actor and his wife Kelly Preston - whose 16-year-old son Jett died after suffering a seizure in 2009 - are devout followers of the faith and he insists he won't be joining those slamming the religion following the airing of documentary 'Going Clear: Scientology and the Prison of Belief' because he has only had "beautiful" experiences.
He said: "[Scientology] has been nothing but brilliant for me.
"I've been so happy with my experience in the last 40 years that I really don't have anything to say that would shed light on [a documentary] so decidedly negative.
"I've been brought through storms that were insurmountable, and Scientology has been so beautiful for me, that I can't even imagine attacking it."
Speaking about the aftermath of Jett's death, he added to the Tampa Bay Times newspaper: "Oh, my god, I wouldn't have made it [without the church's assistance]. Honestly."
The 61-year-old star - who hasn't seen 'Going Clear' and doesn't plan to - claims his faith has helped him to help others and so to speak against it would be a crime.
John - who also has 14-year-old Ella and four-year-old Benjamin with Kelly - added: "I've helped so many people through hard times. Loss of children, loved ones, physical illnesses. Through many tough, tough life situations I've used the technology to support them and help them. It's always worked.
"So, why would I even approach a negative perspective? That would be a crime to me, personally, to do that."