Students at Oxford University are demanding that a Catholic law professor be sacked for alleged homophobia.

More than 400 people have signed a petition calling for John Finnis to be removed from teaching, citing “a long record of extremely discriminatory views against many groups of disadvantaged people” including the LGBT+ community.

Finnis, 78, who is emeritus professor of law and legal philosophy at University College, has rejected the students’ claims, saying there was “not a ‘phobic’ sentence” in all his writings.

His Collected Essays, published in 2011, include an assertion from a paper published in 1994 that homosexuality is “never a valid, humanly acceptable choice and form of life”. It is “destructive of human character and relationships”, he wrote, because “it treats human sexual capacities in a way which is deeply hostile to the self-understanding of those members who are willing to commit themselves to real marriage”.

Migration is another theme in his writing. In a paper published a decade ago, he wrote: “European states in the early 21st century move … into a trajectory of demographic and cultural decay … population transfer and replacement by a kind of reverse colonisation.” He warned of coming “ethnic and religious inter-communal miseries of hatred, bloodshed and political paralysis”.

Finnis, who converted to Catholicism in 1962, has advised the Vatican and mentored the conservative US judge, Neil Gorsuch, who Donald Trump appointed to the US supreme court in 2017.

The students’ petition calls for Finnis to be removed from teaching on the grounds that “university is a place to focus on education, not to be forced to campaign against or to be taught by professors who have promoted hatred towards students that they teach”.

The students also want Oxford “to clarify its official position on professors who have expressed discriminatory views and behaved in discriminatory ways, especially those who have shown obvious hatred and intolerance”.

Finnis told the Oxford Student: “I stand by all these writings. There is not a ‘phobic’ sentence in them. The 1994 essay promotes a classical and strictly philosophical moral critique of all non-marital sex acts and has been republished many times.”

The professor told the Guardian by email that his critics “mistakenly take arguments against their positions and choices to be offensive to them as persons”. The problem was made worse by “paraphrases and mutilated quotations”.

He added: “It’s clearer than ever to me that the positions I’ve been criticising are damaging to children and other vulnerable people, and to the sustainability of societies.”

Freedom of expression was “threatened by recent notions of ‘hate speech’, ‘phobia’ and so forth”.

He said: “Advanced students of legal and political theory take it for granted that there is educational value in engaging critically and carefully with arguments and theories like mine. That is why I am still being invited to give seminars nearly a decade after my retirement from Oxford.”

Alex Benn, one of the authors of the petition, said Finnis had “built a career on demonisation”. Benn added: “His so-called arguments about disadvantaged people are hateful, not to mention widely discredited.”

Benn told the Oxford Student: “Campaigns like this one often receive simplistic responses calling for tolerance or academic freedom. But law, employment and education already draw boundaries about what won’t be tolerated. The humanity of disadvantaged people, including LGBTQ+ people, isn’t a debate … I started this campaign not only to address the specific issue of Finnis’ role at Oxford, but to get Oxford to make up its mind – either it’s in support of equality or it’s not.”

A university spokesperson said: “Oxford University and the faculty of law promote an inclusive culture, which respects the rights and dignity of all staff and students. We are clear we do not tolerate any form of harassment of individuals on any grounds, including sexual orientation.

“Equally, the university’s harassment policy also protects academic freedom of speech and is clear that vigorous academic debate does not amount to harassment when conducted respectfully and without violating the dignity of others. All of the university’s teaching activity, including that in the faculty of law, is conducted according to these principles.”