I should be clear that I agree with the sentiment of the Burning Man saying as it applies to Burning Man and events like Burning Man, I was just nitpicking the language of the curator. I happen to be part of a group that sometimes hosts events and it does feel like a faux pas when somebody asks if they can 'just watch.'
But I think it goes to show the weakness of the analogy with social media, because participation and observation are very much different things on the internet than in person. I think that's a net benefit, because people can observe (and learn) without intruding in most cases.
While there's nothing wrong with lurking (I think we all mostly lurk in low commitment subjects and are active in a much smaller amount of things that really interest us), it presents a fairness of effort and commitment to require participation from everyone.