One of the most recognizable songs of the 1960s, released at the very end of 1966 by Buffalo Springfield, it straddled the line between pop rock and folk rock, between radio friendliness and countercultural legitimacy. Its guitar riff seems to be composed for launching montage scenes of the 1960s. It was the only song by Buffalo Springfield that made the Top 40, at #7, but that was enough fame to launch the careers of Stephen Stills and Neil Young.
So there is something happening here, but what it is ain't exactly clear.
In retrospect, this was a song about Vietnam War protests. In 1967, when the song hit its peak, the Summer of Love was just beginning, and the ugliness of 1968 was a ways away. In various interviews, different explanations for the song's genesis can be explained. It is reputedly a song about a specific protest about music venues in Los Angeles, not a wider comment on society. But the song perhaps was a bit prescient. Certainly, it is hard to listen to it now and not think about wider events.
Even as the song is dramatic, it feels elusive. The lyrics are ambiguous. I always took "People carrying signs, mostly say 'hurray for our side'" to be a comment that there were many people protesting in favor of the war, at that time, but it could also just be that people in a protest obviously support their own side.
And as a song about protest, it engenders not a sense of riotousness, but of caution. This isn't meant to inflame passions, but make us think. The point of this song is to make us "Stop!" and listen. The song presents a tension between emotion and reflection, and that is probably what make it interesting even 50 years later.