Why does mond say old and beautiful things are forbidden?

This is one of the underlying themes of this novel. The society in Brave New World is devoid of meaningful emotion. This allows them to theoretically escape emotional pain. Feeling blue? Just take a prolonged narcotic Soma holiday. Mustapha explains that the people would not understand anger, sadness, passion or tragedy; they are just "blissfully ignorant." Old things or high art (like Shakespeare) entice people to actually feel (shades of Orwell's 1984?) there by destroying the need for anything new. Mustapha figures this inhibits progress.

Huxley wrote this in 1931 however our own society operates on a similar premise. We are encouraged to throw old things away (when was the last time you had your shoes repaired?). We have been indoctrinated into buying new things to consistently validate our very existence. It is an interesting parallel to the novel.