Now, being born 10 years after the event, my information need be taken with a grain of salt as well, but I remember reading somewhere (I wish I could properly attribute it) that the warning about the brown acid had nothing to do with it being bad acid, but that it just too damned potent for most people. In my experience, tripping too hard is the easiest way to get your tickets for a bad trip.

The unfortunate side effect of making the announcement, obvious if you've done many psychedelics, is that everyone who was, until the announcement, happily dosed on the brown acid was suddenly plagued by the bad-trip-inducing ideas of possibly being poisioned, brain damaged, or never being able to come back down. A bit of a self-fulfilling prophecy.