In the early 60s, we'd had "sit-ins," when civil rights advocates quite logically made a protest out of sitting at lunch-counters where black people had been excluded. The "-in" suffix got attached to "teach" when the Students for a Democratic Society held a teach-in at the University of Michigan in March 1965. The "Be-In" of January 14, 1967 preceded the "love-in" and the TV show "Laugh-In."
In the hippie era, the idea that we could simple "be" felt — often with the prompting of LSD — so right. To hold an event that was patterned on a protest with that "-in" but at which you would just be... well, it was very 1967, as was the delight at the cosmic pun on "human being." Remember, this was before hippies seemed dumb. Imagine a time when hippies felt like the cutting edge of enlightenment:
The Human Be-In focused the key ideas of the 1960s counterculture: personal empowerment, cultural and political decentralization, communal living, ecological awareness, higher consciousness (with the aid of psychedelic drugs), acceptance of illicit drug use, and radical liberal political consciousness....California had, only a few months earlier, banned LSD, shutting the door to cosmic perception. Timothy Leary was there to say "Turn on, tune in, drop out." Among the other gurus: Richard Alpert ("Ram Dass"), Allen Ginsberg, Gary Snyder, Michael McClure, Dick Gregory, Lenore Kandel, Lawrence Ferlinghetti, and Jerry Rubin. Yes, there were also women in those days, but it was before prideful enlightened men noticed a need to perform gender-diversity theater. Male human was human enough for the Human Be-In. There is, however, a snakily sexy lady dancing in the audience in that video.
Hells Angels provided security. Jefferson Airplane, The Grateful Dead, and Big Brother and the Holding Company, and Quicksilver Messenger Service played music. There was "White Lightning" LSD from Owsley Stanley and free turkey provided by the Diggers.
The serious adults who ran the mainstream news and covered the Human Be-In didn't think they were running free ads for LSD and the counterculture but they were. And those ads were vastly more effective than ads for conventional trips to tourist destinations. We teenagers watched and dreamed of making it out to San Francisco where life was beautiful and love was everywhere.
ADDED: "There was an awakening going on, and we knew it was happening across the country, and we knew there were pockets of people out there who felt isolated and alone and scared. We wanted to send a signal out to them: 'Hey, it’s OK to come out and spread your wings. Be your fully glorified self in all your beauty and joy. … You are not alone.'"