Many people think about that the past building has to destroy. because of the society scenery. Also many experts claim that the society scenery will be change for every 10 years. but in my opinion, government has to protect the ancient building.
First, the past architect skill will be a good based for modern building skill. modern architecture learns many skills from the old building. for instance, in Korea, variety architectures build traditional Korean building called hanok. as you can see in this example, the past building will be a good learning material for future architecture.
Second, past building should be a vital tourist attraction. many tourists finds some places that represent the history of that country. for example, if you are searching some places in internet, they will show the building that very old and impress. It shows that the past building would be an important tourist place.
Lastly, the past building can be an identity of that country. for example the Eiffel Tower is the landmark of Paris, and the Great Wall of China is the identity of China. As you can see in this examples the old building could be a identity of that country, it will be a vital property.
In conclusion, the past building helps the modern architecture to learn more high level skills, and it could be the vital tourist attraction. also the past building could be an identity of that country. so for these reasons, in my opinion, the past bulling is the vital material for future architect society.