Yes, the US government's fair use on copyrights is a good thing, because it allows for the work to still be a part of public discourse. If there were no fair use, society could not even discuss the copyright works. There needs to be some flexibility in copyrighted works, so that people know they discuss the works and do satire with them, without violating copyright laws.
The reason why fair use copyright is beneficial is that it prevents companies and individuals from using the idea of copyright as a way of silencing criticism. For example, let's say a studio puts out a terrible movie. If you posted a negative review that used a movie poster or some small movie clips, the studio could try to slap a copyright infringement claim on your review to keep it from getting out. However, with the fair use clause, the studio would not be able to do this, since fair use allows the usage of other people's content for educational, review, and other types of limited purposes.