The purpose of art is to inspire, the purpose of knowledge is to educate.
Overzealous attitudes to copyrighting work turns these things into nothing more than commercial venture, and is detrimental to the advance of culture and knowledge—greed is destructive.
Greed seems to be the common motive behind the modern obsession with copyrighting of just about all work, and with extremely restrictive conditions—not just to protect it, not merely to obtain suitable reward for one's work, but to extort the maximum amount of money that's possible from selling encumbered access to it. We are going to lose some valuable material because copyright disallows it being copied it for a long period, and the passage of time will make it uncopyable (as it deteriorates, or a change in technology renders it unreadable), or it's simply forgotten about.
By comparison, some of history's greatest art has inspired other artists who've partially copied it, or its style, while adding their own embellishments, because they could do so. And this was considered a compliment to the original artist, not stealing—classical artwork and music is replete with examples of this.
Many important discoveries are found through the pooling of knowledge, and we learn by sharing what we learn, but that process is harmed by restricting the information—whether that be because of copyright, or unaffordable costs involved in purchasing copies.