Mr. Nehru had good cause for caution. During the volatile 1940s, during which India won its independence from Britain, he saw how Islamism posed an existential challenge to the nation’s unity, and Communism to its democracy. Pakistan was born in 1947, at the same time as India, becoming the first Islamic republic of the postcolonial era. A year after that, the Communist Party of India, instead of joining Mr. Nehru’s efforts to build up the fledging Indian nation, declared its independence a “fake” and began an armed struggle.

By 1951, that red revolution had mostly died out, partly because of limited popular support and because Moscow, which backed Indian Communists, was wary of alienating Mr. Nehru as the Cold War was picking up. Yet some Communist sympathies continued to smolder. In 1962, when India suffered a devastating defeat in a war against China, a powerful section of Indian Communist leaders backed China. They were imprisoned, briefly, and in 1963, the Nehru administration clarified the scope of free-speech laws.

Within a few years, India’s Communists had split three ways. Two parties joined the nationalist mainstream; the third, which identified itself as Maoist, started a violent revolution to overthrow the Indian government. Many of that group’s younger followers found sanctuary at universities, knowing that by longstanding tradition, the police were loath to enter campuses.

But as the violence grew more intense in the 1970s and thousands of people died throughout eastern and northern India, police forces began crossing university gates to arrest Maoist radicals. Then in the 1980s the old specter of religion returned to haunt India: In Punjab, demands for the creation of a separate Sikh state turned into a full-fledged insurrection, which encouraged Muslim separatists in Kashmir to rise up as well.

Many Indians today are still wary that religious separatists and Maoist extremists continue to threaten India’s unity, and that they have supporters among students. Some try to explain away such activism by pointing to anti-Vietnam War protests at U.S. universities in the 1960s and 1970s. But to do this is to overlook the scars that terrorism’s long and lacerating history in India has left on us here. Mr. Afzal, whose rights the J.N.U. students were rising to defend, was involved in the 2001 terrorist attack on India’s Parliament. I wonder how Americans, after 9/11, would react to a “cultural evening” celebrating Osama bin Laden.

Some reactions to the J.N.U. protest were ugly. A group of lawyers assaulted the students who came to court to face charges of sedition. A videotape of a speech made by the most prominent J.N.U. student leader reportedly was doctored in ways designed to incriminate him. Such things are unacceptable.

But many Indians are livid about one thing that is not in dispute: that some of that talk on Feb. 9 was aggressively secessionist. As Mr. Nehru himself well understood, freedom of speech is not a license to undermine the sovereignty and integrity of India.