In the past, there was only one acceptable form of ballet, which was classical ballet. However, ballet has evolved a lot more since then. As a result, there are many different forms of ballet today, such as classical ballet, romantic ballet, neoclassical ballet, and contemporary ballet. All of these have their own advantages and disadvantages, which is why each of them holds an important place within the art of ballet and none of them should be forgotten.
Firstly, from a historic perspective, it is very important to keep dances and ballet forms of the past alive, as it is interesting for a modern audience to see how ballet and dance were performed in the past.
Secondly, it is also a question of personal taste and preference. Even nowadays, there are people who prefer classical ballet to modern ballet. Just like classical music, classical ballet might not be fashionable as much anymore these days, but it is still an art form adored and loved by many. This is the case for many forms of art. Take paintings, for example—just because there have been changes of trends and a rise of modern artists, this does not mean that great artists of the past, such as Rembrandt or Da Vinci, should be forgotten. Likewise, music has moved on since the times of composers such as Beethoven and Mozart. However, this does not necessarily mean that they should be forgotten about now that we live in a world of new forms of music, such as pop and rock.
The same philosophy applies to ballet—there is no reason to have to decide between the old and the new; they can happily coexist next to each other, as there is room for both. There will always be people who prefer the old style, and likewise there will always be people who prefer the modern style, just as there will be people who like and appreciate both.