Nobody likes to land at a foreign airport and get arrested, but thanks to a new Scottish law any American who touches down at Edinburgh’s international airport risks a mirthless flirtation with law enforcement. The reason is that Scotland’s new Hate Crime Act has come into effect — and anyone who runs afoul of it could end up in the clink.

The law, championed by Scotland’s first minister, Humza Haroon Yousaf, makes it a criminal offense to “stir up hatred” against “protected characteristics” that include “race, colour, nationality (including citizenship), or ethnic or national origins … age, disability, religion or in the case of a social or cultural group, perceived religious affiliation, sexual orientation, transgender identity [or] variations in sex characteristics.”

Henceforth if something that is said to one’s spouse, or posted on Facebook, or even written in a private Whatsapp chat can be construed to be “stirring” hate, the presumed offender can be prosecuted. That was confirmed by Scotland’s minister for victims and community safety, Siobhian Brown, who said on Monday that people “could be investigated” for the offense of “misgendering” someone online. 

In an act of preemptive defiance, the British author J.K. Rowling came out swinging against the new law. Ms. Rowling, creator of the Harry Potter books, wrote on X, “I’m currently out of the country, but if what I’ve written here qualifies as an offense under the terms of the new act, I look forward to being arrested when I return to the birthplace of the Scottish Enlightenment.”

Lest there be any doubt that the culture wars are now raging at a high tide in Britain, Prime Minister Sunak wasted no time in wading into the fray, swiftly coming to Ms. Rowling’s defense. “People should not be criminalized for stating simple facts on biology,” Mr. Sunak stated on Monday. 

Ms. Rowling is not a stranger to this debate. She backed protests against Scotland’s ill-fated Gender Recognition Reform Bill, which would have allowed people aged 16 or older in Scotland to change the gender designation on their identity documents by self-declaration. The legislation, which was supported by Mr. Yousaf’s predecessor, Nicola Sturgeon, was successfully blocked by Westminster in December. 

On Monday, Mr. Yousaf said that he was “very proud of the Hate Crime Act,” adding that it would “protect people from hatred, while at the same time protecting people in terms of their freedom of expression.”

Ms. Rowling is having none of that. 

On Monday the famous author also shared her opinion on X that “the re-definition of  ‘woman’ to include every man who declares himself one has already had serious consequences for women’s and girls’ rights and safety in Scotland, with the strongest impact felt, as ever, by the most vulnerable, including female prisoners and rape survivors.”

She added, “It is impossible to accurately describe or tackle the reality of violence and sexual violence committed against women and girls, or address the current assault on women’s and girls’ rights, unless we are allowed to call a man a man. Freedom of speech and belief are at an end in Scotland if the accurate description of biological sex is deemed criminal.”

Other, non-famous opponents of the legislation have warned that not only could it impinge on free speech but also that it could be used to settle scores. At a protest held Monday outside the Scottish Parliament House, Holyrood, some demonstrators appeared with tape over their mouths and held placards that bore messages such as, “Dear SNP, ‘diversity’ doesn’t mean that only people you agree with can speak.”

Mr. Sunak, for his part, has clearly spoken up. The prime minister stands squarely in the opposite camp from Mr. Yousaf’s social democratic Scottish National Party. The Tories still call the shots at London despite the party’s declining popularity ratings. It was not immediately clear if the new Hate Crime Act could yet be defanged as was the gender reform bill.