Earlier quoted context omitted.
I've personally had this play out with a number of services. LastFM comes to mind. I really enjoyed having a persistent record of what I listened to for my own use and for finding new music. However, I stopped using the service because, honestly, I'm not exactly proud of every song that makes it to my most-played list. LastFM let's you remove a song from your profile if I remember correctly, but it was easier to not…
"I'm not exactly proud of every song that makes it to my most-played list." It would be very interesting for me if you might write up a few lines on "why", if you can.
Very few systems make it easy to manage multiple (and shifting) sharing relationships, so not sharing by default is the easiest thing to manage.