There may be many reasons to keep a book around, but "contains terrible ideas dismissed for really good reasons" is not one of them.

Actually, even that is. "Really good reasons" are things you want to keep track of. When they're really good reasons against something, you want to keep track of the thing they're against to fully understand the good reasons.

Intellectual history is a series of arguments. If any institution should remember and analyze the bad arguments, it's academia. Consigning them to the memory hole loses information about the good arguments as well as the bad. That goes beyond the historical argument - that's an argument based on information loss regardless of historical circumstances.