There are generally two types of reasons why old buildings should not be torn down. The first reason is that they may have artistic merit. The second is that they have historical importance. It is certainly possible to argue that the Chartres Cathedral qualifies for preservation on both counts.
We can definitely argue that the Chartres Cathedral is worth saving simply for its beauty. The cathedral was one of the most important art forms of the High Middle Ages. These buildings were supposed to be testaments to the importance of God in the lives of the people of the time. Therefore, they were made to be as beautiful as possible. The Chartres Cathedral is beautifully preserved and has barely been changed since it was built in the 1100s. It is a wonderful example of a beautiful form of art and should not be torn down any more than something like the Mona Lisa should be destroyed.
We can also argue that the cathedral is so historically significant that it deserves to be preserved. Part of the reason for this is alluded to in the previous paragraph. This cathedral is an important testimony to the importance of religion in the lives of medieval people. It helps us to understand how they thought. Since there are so few cathedrals remaining in such good states of repair, we should preserve it as a piece of history. In addition, the cathedral at Chartres was accompanied by an important cathedral school. It was at the Chartres cathedral school that the new system of education was created. This system included the trivium and the quadruvium and it was the basis for all higher education beginning in the medieval period and continuing into the Renaissance.
Because the Chartres Cathedral is beautiful, and because it is historically significant, it should not be torn down.