I think Wendy Kaminer is correct that there's a problem when credit for words that are written by someone else flows to the person who speaks them, or under whose name they have written. It implies a skill set they don't actually have, and if they're a politician, can enhance their career as a result. But I think she's a bit off in the reason that people end up buying those ghostwritten books.
When one purchases a clearly ghostwritten book by a political or celebrity figure, I think most folks are doing it entirely without interest in the quality of the prose or the arc of plot. Rather, they are doing it because the book gives them the sensation of contact with and access to the book's subject, no matter how fleeting and mediated. It's a different impulse than the one that leads us to pick up novels, or poetry, or books by non-fiction writers we know and love. It's really genuinely not about the prose, or the structure, or the character development.