I’m in England right now, home to both of the sights above: the polite request to “please keep off the grass”, accompanied by tiny iron hoops; and the forbidding walls surrounding the gardens of Buckingham Palace. The former encapsulates everything which people like about England; the latter is the dark and regrettable side of things.
Now imagine that both of the gardens above were open to anybody paying an annual membership fee. The gardens on the left would have many more freeloaders — people who just saunter onto the grass and enjoy the sunshine without paying. The ones on the right would be much more effective in keeping such people out.
But here’s the thing about freeloaders: if they value what they’re getting, a lot of them will end up paying anyway. What happened when the Indianapolis Museum of Art moved to a free-admission policy? Its paid membership increased by 3%. When the Minneapolis Institute of Arts did the same thing, paid membership increased by 33%.