Sussex, England: a philosopher cowers as masked figures set off flares. Yale University, USA: "you are disgusting, step down," a student screams at a college president. Berkeley, California, USA: riot police patrol the streets as a controversial speaker arrives at a student meeting. 

An ugly row over free speech is slowly unfolding at university campuses across the world. For years, furious incident after furious incident have dominated the headlines.

This time, it is Sussex University in the spotlight. A philosophy lecturer, Professor Kathleen Stock, is accused of transphobiaDislike or prejudice against transgender people.  by students. Stickers have appeared, calling on the university to fire her.

The university backed her, but her union did not. Their lack of support, Stock says, has "effectively ended" her career.

Now an MP, Shadow MinisterIn the UK, a shadow minister is a member of the opposition party who would hold office if their party was in power. Shadow ministers scrutinise the actions of government ministers.  for Women and Equalities Taiwo Owatemi, has entered the fray. The lecturers' union, Owatemi says, are "strong and principled". Meanwhile, Sussex University must remember its commitment to protect transgender students.

But what exactly is at stake here? 

Both groups say they are defending a principle. On one side is Professor Stock. This year, she published a book questioning the idea that gender identity is more "socially significant" than biological sex. She argued that single-sex spaces should be reserved only for cisgenderA person whose gender identity matches their sex assigned at birth. The term was first used in academic articles in the 1990s. women.

Stock's supporters say that whether or not you agree with her views, the principle of free speech means she should be allowed to express them. Hearing controversial opinions is a vital part of the university experience.

On the other side are pro-transgender activists. They say they are fighting to protect the rights of transgender people. 

For many, this row is bigger than just one professor and one university.

"Truth in a democracy must emerge from conversation," said one journalist. "All the great causes of the civil rights movement were taken up in the public realm and the argument was heard. It was won by persuasion, not cancellation." 

"Dissent, disagreement, debate and peaceful protest are fundamental to any democratic society," added the UK universities minister after Stock received death threats.

But not everyone agrees that Stock should be protected by free speech rules. Today, we do not believe people should have the freedom to say that one race is superior to another, or that the HolocaustThe murder of six million Jewish people in Europe by Nazi Germany. Members of other minority groups were also killed. did not happen. Society, and the lawA rule that everyone must follow. , maintains a divide between free speech and hate speech.

Some think that Stock's views cross that line. "The anti-gender ideology movement is at once anti-feminist, homophobic and transphobic," wrote gender theorist Judith ButlerA world-renowned philosopher best known for her book Gender Trouble. last month. 

"The category of woman can and does change, and we need it to be that way. Politically, securing greater freedoms for women requires that we rethink the category of 'women' to include those new possibilities." 

Definitely, say some. Freedom of speech is not just about listening to views everybody agrees with. Campuses must be a space for open debate. Universities who fail to support academics with controversial opinions are failing to uphold one of the founding principles of the democracy we live in. 

This is ridiculous, say others. Freedom of speech is important, but it is not without any limits. Professor Kathleen Stock's arguments go beyond those limits. Universities' first responsibility must always be to protect their students, especially vulnerable or minority groups.