The pontiff criticised the "utopia of the neutral" in his comments to the Pontifical Academy for Life, the Vatican's bioethics advisory board, taking up his criticism of so-called gender theory and the idea that people can choose their sex.
The academy under the previous two popes represented the leading, hard-line voice of the Catholic Church on sexual ethics, morality and culture war issues such as abortion and euthanasia.
Francis has revamped it to broaden its scope to better reflect his holistic view of human life in concert with creation.
But Francis kept to the church's hard line against gender theory in his first meeting with the new members on Thursday, lashing out at how today's exaltation of individual choice extends to one's gender thanks to technological advances.
"Rather than contrast negative interpretations of sexual differences ... they want to cancel these differences out altogether, proposing techniques and practices that render them irrelevant for human development and relations," he said.
Such practices, he said, "risk dismantling the source of energy that fuels the alliance between men and women and renders them fertile".
While Francis has strongly upheld church teaching on abortion and other life issues, he has not emphasised them as much as St John Paul II or Pope Benedict XVI.
Instead, he has sought to broaden the church's definition of what it means to be "pro-life", stressing for example the need to guarantee dignified respect for the elderly, people at the end of their lives, and not just focus on the unborn child.
The head of the academy, Monsignor Vincenzo Paglia, said this week that "pro-life" is more than just a bioethical and theoretical concept about a hot-button issue like abortion, but also includes human issues like migration, the environment and even arms trafficking.
Being pro-life, he told a news conference, "means promoting a culture that helps life wherever and whenever".
