I believe that fair use should be defined legally and thoroughly to avoid useless legal battles. The economic problem, fundamentally, is that fair use is a type of expropriation of the creators' intellectual property.
We have to find a way to compensate fair use. Some might think that the user is not the one who should be paying royalties for the work used, or that someone else should pay.
When we have or add exceptions, even when we add “such as”, as someone else has suggested, or we tack on other exceptions to copyright, we expropriate creators' intellectual property without giving them any compensation.
In economic terms, the problem is that we have to decide who else should pay the authors, the composers and the artists, the rights holders and the creators for fair use.
The principle of fair use is not problematic in economic terms. It becomes a question of compensation. Someone has to pay, but who?