The 'Battle Scars' hit-maker recently revealed that he had moved away from the Christian movement that shaped his youth.
"My views are more based on life and discovery and research than just what I'm told," he told the Daily Telegraph last week, adding that he still believes in God.
The 30-year-old singer announced that his beliefs began to change when a friend at church fled the country after revealing he was gay, fearing that other church-goers would judge him.
"My friends and I were like, 'Dude, why did you leave, what did you think we would say?' It became not a big deal at all," Guy told the Daily Telegraph last week.
"Look at gay marriage. I don't think anyone has the right to tell someone who they can and can't be in love with."
Yesterday, Guy posted an open letter on his Facebook page in response to negative comments from some religious Christians on social media.
"I have grown a lot in the last few years, due mainly to my marriage to Jules and then being blessed with [seven-month-old] Hudson this year. I have come to appreciate people and life a lot more," he wrote.
"It saddens and concerns me for the sake of my child that we live in a world still full of intolerance, hatred and prejudice. Hudson is the inspiration for me to write my latest song 'Get Along' as I want to do what I can to make a positive impact in the world."
"I understand how it's possible that a minority of extremist religious organisations had encouraged some members to behave in unreasonable, socially unacceptable and even violent ways.
"Dogmatic teachings invariably lead to such outcomes. However, I do think this is the minority and not what most people in the world want. But it seems societies around the world are becoming more aware, educated and open-minded, and are evolving as I am also evolving to embrace a deeper spiritual understanding about life rather than mere submission to rigid rules."
Guy added that "religion is a very personal thing", and made a plea for people to respect one another's different beliefs and faiths by finding common ground.
More than 7500 people have liked the post so far. Guy has more than 195,000 Facebook fans. For the full letter, visit Guy's Facebook page.
His new album Armageddon out now.
Check out our recent interview with him below:
Flashback: Guy's first audition tape for Australian Idol in 2003
In pics: Before they were massive: Reality stars' first audition tapes
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