Venice is really a fairly small place, and definitely has limited capacity to handle tourists. I can definitely see limiting the number of day visitors here, although I don't know that completely banning all of the cruise ships is their best solution. Today the business of Venice is tourism. Without tourists, it would not survive.
The issue of the ships is somewhat different from the number of tourists issue. because of their sheer size, they change the currents, channels and sea life of the islands in ways that would be different if anchored on other shores of the lagoon. Plus, at anchor in Venice, they tower over the buildings.
Ships have lots of different ways of getting their travelers to a destination, if they can't dock there. Smaller boats to shuttle people back and forth are very popular with tourists and the cruise companies, and would work well here.
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