They're not the only ones concerned about the deal. Some writers resent what they feel is an opaque agreement negotiated by the Author's Guild that takes control of their copyright unless they specifically opt out.
The deal centers around "orphaned works." These are books that are still protected by copyright but are out of print. Currently Google indexes these books but doesn't show any of their contents. Google wants instead to automatically show all of these books unless the rights holders opt out. In return, they'd share 63% of any revenue they earned from advertising or access fees. Google would also establish a rights management group for the works.
One of the reasons there is no competition on this agreement is because Microsoft abandoned their book search project last year. However, concern over antitrust may end up broadening the agreement with the Author's Guild, which will likely make even more authors feel like their copyright is being negotiated away without their permission.
Another alternative is an opt-in system where authors and rights holders must request their works to be included. Such an agreement is likely to be more popular with everyone but Google.