Photograph: Michal Daniel

Despite the ecstatic, uplifting dance party that ends the Public Theater’s triumphant revival of Hair—cast members invite eager spectators onstage to revel under the stars—one leaves depressed. The reason is twofold: First, 41 years after the debut of this epochal musical which glorified peace and love, the U.S. is again stuck in an unjustifiable imperialist quagmire. Second, we have no radical antiwar movement comparable to the one that inspired Hair. Apparently, we also used to fly to the moon. Are we evolving backwards?

Maybe I’m just being a square bringer-downer. Hair is without reservation a welcome acid flashback to a time in which cynicism kept pace with idealism and the American Dream was still something that could be taken seriously enough to be trashed by a bunch of dirty, irreverent hippies cavorting in a park. What comes across now is the tragic undertow beneath the youthful exuberance and authority-tweaking. And the piece’s quaint, vaudevillian structure is striking, peeking out under love beads, motley costumes and yards of tonsorial kudzu. Galt MacDermot’s wildly energetic rock-pastiche score and James Rado and Gerald Ragni’s book and lyrics remain inspirational and wisely witty.

Some commentators may scoff that these hippies are too scrubbed to be dangerous, but director Diane Paulus has done a phenomenal casting job (retaining most of the cast members from last September’s concert at the Delacorte). From goddesslike Patina Renea Miller’s soul-stirring “Aquarius” to Will Swenson’s buff, bluff Berger and Jonathan Groff’s raw-hearted Claude, these fiercely talented young actors leap clear over the generation gap to deliver a mystic vision we sorely need. Add Karole Armitage’s pulsating group choreography and a supremely groovy band, and the moon is smack dab in the seventh house. Us, we’re in seventh heaven.