Maurice Williamson, the New Zealand MP for Pakuranga whose pro-equal marriage speech went viral, has written an open letter to Australia and the rest of the world in defence of same-sex marriage.

Gay rights debate in Australia has recently been reignited by former Prime Minister Kevin Rudd’s declaration that he has become a supporter of marriage equality. In an article for The Australian, Mr Williamson urges his country’s closest neighbour – and the rest of the world – to legalise same-sex marriage without fear of consequences.

“It’s great for those it affects but for the vast bulk of people it will have no impact on their lives,” he wrote. “All gay marriage does is allow consenting gay couples to get married. That’s it. I would say to the countries yet to have the gay marriage debate: Be Ye Not Afraid.”

Mr Williamson wrote: “You might have seen there was rioting in France after they passed similar legislation. Not in New Zealand. People just carried on with their lives, as I suspected they would.

“Now, if that’s what the prophesised ‘gay onslaught’ looks like then we’ll take it every day and twice on Sundays.”

The speech Mr Williamson made in parliament following the final reading for the bill to allow equal marriage was hailed by Gawker as “a speech for the ages”, and quickly went viral on social media and other sites.

During the “big gay rainbow” speech, he said: ”I had a Catholic priest tell me I was supporting an unnatural act. I found that quite interesting coming from someone who has taken an oath of celibacy for his whole life.”

Mr Williamson said he has since had “a few people writing nasty letters to me about the speech”.

“One man hoped my family and I would get AIDS and die,” he wrote. “Many others said the Lord would deal to me in time – not very Christian of them is it?

“One letter went on to say that soldiers who fought in wars would be outraged at what had happened – but this too is a flawed argument, as those soldiers were fighting for freedom.”

Ultimately, he said, the “fear mongering” put forward by opponents had been unfounded: “In all the hate-filled emails there was not one credible argument about how allowing gay marriage would affect my marriage or theirs. Because in the end it won’t.”

New Zealand’s MPs broke into song as they passed the same-sex marriage bill 70 votes for and 44 against in April.