Mr. Goldberger, now 79, adored the A.C.L.U. But at his celebratory luncheon in 2017, he listened to one speaker after another and felt a growing unease. A law professor argued that the free speech rights of the far right were not worthy of defense by the A.C.L.U. and that Black people experienced offensive speech far more viscerally than white allies. In the hallway outside, an A.C.L.U. official argued it was perfectly legitimate for his lawyers to decline to defend hate speech. Mr. Goldberger, a Jew who defended the free speech of those whose views he found repugnant, felt profoundly discouraged. “I got the sense it was more important for A.C.L.U. staff to identify with clients and progressive causes than to stand on principle,” he said in a recent interview. “Liberals are leaving the First Amendment behind.”