What made the cocktail so good was expressed by William Boothby in his 1908 book:
"The idea of making any liquor into a cocktail was conceived only for the purpose of removing the sharp, raw taste peculiar to all plain liquors."
That is the beauty of a cocktail. In its purest form, it is nothing but a slightly-sweetened, slightly diluted way to drink any spirit with bitters. The bitters remove the harshness of the ethanol and provide an accenting flavor. If you make your own bitters, be sure that they provide both functions. But I digress.
A true cocktail is a thing of beauty if it is made with good spirits. Cocktails were so pleasing that the word became too trendy for the good of the drink. When a word is expanded to mean everything, it begins to mean nothing.
Whenever I witness someone calling all drinks cocktails, I feel that they do not understand what makes a true cocktail special and different from a punch, for example. To hear a mixologist or bar professional use the word cocktail haphazardly makes me feel the same way the trained cook in me would feel if I heard a 'foodie' describe all Asian food as 'sushi.'
For a bar professional to use terminology that does not reflect what makes each genre of drink satisfying in its own right suggests to me that they do not really know very well how to achieve those ends. Such people are more often than not referring to a punch and make very few true cocktails. This is not to say that cocktails are always better or more appropriate to the setting and time than are punches, or any other type of drink. As professionals, we should know the differences so that we may make the most appropriate type of drink at that moment.
It is true that the word 'cocktail' has been mis-applied by the uneducated for a long time. It is true that the debased 'mixed drink' meaning of the word can be found in dictionaries. Some have said that this is a hopeless effort. But, without understanding the elementally-different types of drinks possible, they are bound to all become some sort of punch at the hands of the unenlightened.
This is a worthwhile effort, and one inspired by Pluto. For a very long time, Pluto was categorized as, and called, a planet. The scientific method then proved it wasn't a planet and announced it to the world. Sure, many laypersons still consider Pluto a planet, but all of the people who matter in the world of science and publishing know better and speak and write accordingly. 'Cocktail' is my Pluto.
If you are a student or client of mine and I add, "and other drinks" after you loosely use the word 'cocktail,' please don't take it personally. I once labored under the same sloppiness and ignorance. I admit that I am a little radical about it. This is just one of the reasons I (perhaps-foolishly) shy away from the so-called "Tales of the Cocktail" each year.