Embattled students at the University of California, Berkeley tried, but failed, to cobble together an event to be billed as “Free Speech Week.” Beginning Sunday, it was to feature several panels with controversial speakers. Provocateur Milo Yiannopoulos, whose appearance at Berkeley over the winter prompted violent anarchist riots outside the venue, referred to it as “our Woodstock.”

The idea of free speech is simple. Students, professors, and administrators are all constantly exchanging ideas on campuses. If the market of ideas is free, the spectrum of ideas is vast and runs the gamut from reasonable to bizarre to dangerous. But dangerous ideas teach us about what is safe. Debate over what constitutes a reasonable idea, be it in politics or science or literature, is invaluable to the process of making that judgment.