The sentence that would weaken the writer's argument if they chose to add it is:
"People who make a big fuss about preferring physical books need to get over themselves."
This sentence undermines the writer’s argument by dismissing the preferences of physical book readers and introducing a tone of condescension. It implies that those who prefer physical books are being unreasonable, which could detract from the writer's overall message about the importance of supporting e-books and acknowledging their benefits, rather than creating divisions between readers.