The Eagles in the 1970's might as well been Barry Manilow,not that i dislike the Eagles but rock n roll shows in the 1970's were full of drugs,it was more common than not to see the band doing drugs & drinking on stage as well as the audience.
Heck,i openly smoked pot,hash & opium at many a concert,for all to see, & i was not alone,the 70's were the drug years for rock concerts, not just Zappa.
I saw the dead in the 70's and early 80's around 75 times,I think
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I also saw most of the "Day on the green" in Oakland,and many many bay area legends in san fran and Sacramento,I saw all the greats,led zep,the who & the dead together,the winters bros,country joe,santana,van morrison,you name them and I saw them,and you name the drug,and I did it back then.I saw shows at the old waldorf,winterland,cow palace,dead new years eve shows,it was a great time for music,and the bay area was the nucleus .
anyway,you are right,in the 70's that was the concert scene.
I am glad I experienced it.I am 51,and the 60's & 70's music was & is my thing.
gladly no more drugs,just beer and tequila now.