I'd be glad to hear anybody's opinion about it, but viewed as a historical question (since that's all it amounts to now) the turning of the youth away from established adult-driven culture, away from safe conformist attitudes, the total annihilation of the 50s consensus Eisenhower Corporate Man Country Club, Golfing, square world, the counterculture emerging as a denial of button-down, repressed America went critical-mass with Bob Dylan in 1965-1966. The Beatles were still singing love songs and the Stones were doing their greaser thing in 65.
Bringing It All Back Home,
Highway 61 Revisited, and then finally,
Blonde On Blonde in '66 changed everything. (not for me at the time, though, I was just 12 and digging the Beatles Love Songs and
The Supremes,
Sam & Dave Herman's Hermits, The Monkeys, etc

and pouring coolade powder on pickles and eating candy). In fact, it was a one-two punch; Hugh Heffner was undermining the foundations from the other side.