The people who took part in the Summer of Love were a minority of the population of 18 year olds at the time from what I understand. Around 100,000 according to Wikipedia[0]

That's not to say that drug experimentation wasn't more widespread than that group: I know my father experimented because he's told me. However he has become pretty conservative as he's gotten older. Or at least supports conservative American politicians and voted for Trump probably both times.

[0]https://en.wikipedia.org/wiki/Summer_of_Love