See? Random people declaring something acceptable or unacceptable without justification isn't particularly helpful. If you want to explain why you find it unacceptable, that might actually be interesting to someone.
I don't mind Amazon knowing how far into a book I've read, if it allows them to better compensate the authors of quality books and helps them penalize the authors gaming the system. However, if you want to keep your reading habits private, I can sympathize with that. An opt-in/opt-out option might be a good compromise in this case.
If you disagree with this practice, you're free to not accept the offer. It's as simple as that.