Well, sometimes they exist for these reasons. Often though ordinances exist because people don't like something and simply want to restrict it without a valid reason outside of personnel preference (as in unreasonable). Like in my city riding a bicycle in the street around our convention center during an event will result in a fine, even though speeds then are so slow as to make riding in the street safer than nearly anywhere else in the city. Never assume an ordinance was enacted for good reason. Always look into them and question them. Especially when they restrict bicycles given the anti bicycle attitude in most north american cities.