US citizens cannot check out books from the Library of Congress (LoC) primarily because the library's mission prioritizes serving Congress and preserving historical records rather than functioning as a public lending library. While taxpayers support the library, its resources are intended for in-library use, allowing individuals to read or study materials on-site. The logistical challenges of lending, such as tracking overdue books and constantly changing inventory, further complicate the idea of a lending system. Users can access public domain materials and make copies, but borrowing is not permitted, similar to how military resources are not available for personal use. The discussion highlights a mix of humor and frustration regarding the limitations of access to such a vast collection.