To quote Stephen Fry quoting Katie Price's manager:

"Katie just tells them what she wants the story to be about, and they just put it into book words"

So, my opinion is that it really depends on how much input the credited writer has in the process. Sometimes they have a good story to tell and need help with the execution. I can be on board with that. (I'm not plugging her or her book, it's just a fun quote)

However, I think it was Reagan who said he looked forward to reading his autobiography someday. That low/no level of input would be on the end of the spectrum where I would not approve of a ghostwritten book.