One of the many legends told about Woodstock is that not only was it a cultural happening, and a pivotal musical event of the era, it was completely free. It was a free festival for people who were into free love. It's actually a true story, but it was by accident more than by design.
The organizers originally intended to charge for entry - because who would put on a festival of this size and make no money out of it? - but had to abandon that idea when the crowd turned up and swamped the field. There was simply no way to organize that many people into queues to buy tickets, so they had to abandon the attempt and let nature take its course. With no organization it could easily have descended into a riot, but fortunately hippies aren't exactly known for their violent tendencies.