A Dutch Roman Catholic Cardinal has said a papal encyclical might be needed to combat false teaching about gender theory.
Cardinal Willem Eijk of Utrecht said high-level teaching from Pope Francis "might appear to be necessary" to counteract modern theories that gender was a question of personal choice rather than determined by biology.
He told Catholic News Service at an interview in Oxford that even Catholic parents were beginning to accept that their own children can choose their genders partly because "they don't hear anything else".
Pope Benedict XVI and Pope Francis had addressed the subject within the past five years, he said. "It [gender theory] is spreading and spreading everywhere in the Western world, and we have to warn people," he said.
"From the point of moral theology, it's clear – you are not allowed to change your sex in this way," he added.
"It is like euthanasia and assisted suicide," Cardinal Eijk continued. "When people first began to discuss them they were unsure," but many people have now become so acquainted with such practices they are now deemed ordinary.
He said many Catholics were now accepting gender theory "in a very easy way, even parents, because they don't hear anything else."
The cardinal – a moral theologian and former medical doctor – was speaking before giving a lecture on the subject 'Is Medicine Losing its Way?'
He told CNS that medical advances were creating a culture in which increased individualism meant gender theory was finding fertile ground. One consequence was a rise in intolerance.
"People are talking about tolerance and they say the individual is free to think what he likes but in practice ... people have to accept this certain view of man, this dualistic view of man and this view of the body as something that is mouldable.
"And when you say perhaps that is not a morally good way, you are excluded," he said. "You have to think according to these modern theories or you are excluded – it's [permeating] the university world, parliament, the mass media.
"It is very painful and they will make it for us Christians ever more difficult, I am sure," he said.