Final answer:
Folk 'purists' objected to Bob Dylan's song 'Like a Rolling Stone' at the 1965 Newport Folk Festival due to his unexpected shift from acoustic to electric performance.
Step-by-step explanation:
At the 1965 Newport Folk Festival, the new song by Bob Dylan that folk "purists" objected to was a) Like a Rolling Stone. The controversy stemmed from Dylan's decision to switch from his usual acoustic performance to a loud electric one. This change was seen as a betrayal by some of his fans who had embraced him as a protest singer and the voice of their generation. Dylan, known for his protest songs and influence on social change, particularly with the anti-Vietnam War movement, had moved away from the expected folk tradition, which sparked significant uproar among the festival's attendees.