This has been a buzz-phrase for a while now. Tends to be trotted out by the libertarian/”classic liberal” (ie reactionary right) “freedom of speech” types – the Peters0n crowd, Jonathan Haidt (a man who claims to be a liberal psychologist/philospher, yet thinks that p0rn is all good fun just like sport and that universities should be held hostage by their wealthy donors to force them to elevate MRA and right wing talking points, he’s a rising star amongst whiny internet adolescents of course) and so on.
Unsuprisingly their idea of “free speech” and “diversity of opinion” never includes standing up for or listening to or giving a platform to women’s point of view: older women, lesbians, disabled women, minority ethnic women, poor women, women who work with victims of male violence, women who have suffered male violence, radical women, separatist women. Even the wrong sort of man is excluded from their brave new free and diverse world, maybe a token nod here and there. Such tiny tiny minds they have.