It's hard to put a finger on the precise effect of a song, however powerful. Howsomever......


How could one say that Where Have All the Flowers Gone? and/or Last Night I Had the Strangest Dream had NO effect in the 60s?
Sure, you can't quantify the effect, but they were right out there with other influences on popular thought.   

Or, during the US Civil War, The Battle Hymn of the Republic?

A song with a strong message, coming at the right time, becomes part of the cultural influences moving in a direction.   That's making a difference, even if you can't hogtie it.

Dave Oesterreich