Every generation needs a Woodstock. Burning man is not real enough.
A massively failed capitalist project that leaves behind an enormous mess?
The ability for people to make a mess on occasion, for whatever reason, is an essential freedom to be cherished and fought for.
Every generation needs an act of rebellion. It's a sort of fundamental law of nature, as a right of passage in a way.
They also knew that crowd control was going to be a problem; instead of hiring police, they brought in people from a commune who were used to doing crowd control for large peaceful gatherings.