One evening last week, just before six, members of the pro-Kurdish Peace and Democracy Party (B.D.P.) gathered in front of the high iron gates of Galatasaray High School, in Istanbul. They planned to march to Taksim Square, about half a mile away, where they would join a mass of protesters. In the square, a range of groups have joined together against Prime Minister Recep Tayyip Erdoğan, and their political and ideological diversity has been held as evidence of Erdoğan’s sweeping unpopularity. But, with some notable exceptions, Kurds, usually Turkey’s most robust anti-government protesters, had been absent.