Are athletes who are born male but identify as female cheating girls? Tennis legend Martina Navratilova says they are.

“To put the argument at its most basic,” she wrote this weekend in an op-ed for the Sunday Times of London, “a man can decide to be female, take hormones if required by whatever sporting organisation is concerned, win everything in sight and perhaps earn a small fortune, and then reverse his decision and go back to making babies if he so desires.”

Her conclusion is blunt: “It’s insane and it’s cheating. I am happy to address a transgender woman in whatever form she prefers, but I would not be happy to compete against her. It would not be fair.”

This isn’t the first time Ms. Navratilova has sounded off on the issue. “You can’t just proclaim yourself a female and be able to compete against women,” she tweeted in December. “There must be some standards, and having a penis and competing as a woman would not fit that standard.” After intense blowback, Ms. Navratilova said she would have nothing more to say until she’d studied the issue more closely.

“Well, I’ve now done that and, if anything, my views have strengthened,” she wrote in the Sunday Times.