I couldn't quickly find the essay, but someone more insightful than me argued that protests were mostly a ritual at this point. They're tolerated because they can't change anything, the system has learned how to shrug them off or repress them if they become inconvenient, so they're mostly about group identity. But I don't think they're useless; Occupy brought the left back into the mainstream, and now socialism isn't beyond the pale anymore. Bernie Sanders isn't exactly Joe Hill, but you don't have to be very old to remember when "socialist" was a snarl word. Protest is more ritual than something that has a concrete effect at this point, but that doesn't make it useless. At the minimum it lets the participants and people who wish they were there know they aren't alone, and knowing I wasn't alone in being more afraid of Republicans than Al-Qaeda sure kept me sane in the early 00s.