Excerpt from this article:
Art museums have watched this development nervously, fearing damage to their collections or to visitors, as users swing their sticks with abandon. Now they are taking action. One by one, museums across the United States have been imposing bans on using selfie sticks for photographs inside galleries (adding them to existing rules on umbrellas, backpacks, tripods and monopods), yet another example of how controlling overcrowding has become part of the museum mission.
…“From now on, you will be asked quietly to put it away,” said Sree Sreenivasan, the chief digital officer at the Met. “It’s one thing to take a picture at arm’s length, but when it is three times arm’s length, you are invading someone else’s personal space.”