From Nat Hentoff's liner notes to "The Freewheelin' Bob Dylan" -

"The first of Dylan's songs in this set is "Blowin' in the Wind". In 1962, Dylan said of the song's background: 'I still say that some of the biggest criminals are those that turn their heads away when they see wrong and know it's wrong. I'm only 21 years old and I know that there's been too many wars... You people over 21 should know better.' All he prefers to add by way of commentary now is: 'The first way to answer these questions in the song is by asking them. But lots of people have to first find the wind.'"

Joan Baez has expressed disappointment that he never 'joined the movement'. But it might have detracted from the Dylan mystique had he actively participated in protest demonstrations back in the 60s.