I think it's a reasonable idea. Who wants the classic and beautiful ambiance of Venice ruined by thoughtless hordes of tourists?
quoted from goitaly.about.com:
While in Venice, Keep Your Shirt On
Venice is one of Europe's most popular vacation destinations and the place in Venice where everyone congregates is St. Mark's Square, called the drawing room of Europe by Napoleon.
St. Mark's Square, or Piazza San Marco, is ringed by the magnificent Basilica San Marco, the Doge's Palace, and several posh cafes including the famous Caffe Florian, popular since 1720. But Piazza San Marco is also home to hoards of pigeons, tourists in all manner of dress lying or sitting around the square, and lately lots of trash from take-away eateries.
In order to return the ambiance of Piazza San Marco to what it was in earlier days, visitors to the square will be asked to refrain from eating in the square (except in the cafes), lying down, camping out, or walking around the city shirtless. According to Yahoo News, while there won't be fines for these infractions, there will be nicely dressed stewards to explain these rules to those who break them.