If you set Would you like to share your ratings and tags with other users? in your preferences to `no' then your tags are not shared and your ratings are still used for predictions
While true, that means the rest of us are at the mercy of each other user to set their preferences that way. And those most likely to set the preference to not bother others are also those most likely to have used tags responsibly in the first place.
Thus your 2nd suggestion to allow mass voting down of bad tags is more likely to be the effective one.