I am sad about this but can understand it. Venice is a beautiful city and one of my favorite destinations. However, it has become overrun with ships. While this has been a boom for small business owners it hasn't really helped hotel, restaurant, higher end shops and other businesses too much.
It is also a not too pretty to continuously see cruise ships going in and out of the canal. Yes, cruise ships are neat and we all love them but they can become an eyesore after awhile.
While we were walking on the opposite side of St. Marc's square "near San Giorgio" the wake of a ship almost came over the embankment and onto the sidewalk. There has to be quite a bit erosion caused by the big ships.
As David said: "Venice is not a large city." Multiple cruise ships put a lot people in a fairly small area.