As a user, I do agree that a "blanket opt in" button/ default checked checkbox is so pointless that it could as well be left out.
A EASILY DIGESTIBLE page explaining what data is stored and how it is used , with an agree button at the end (and separate opt-in for different sets of data/functionality) should be mandatory.
Emphasis on the easily digestible, because we all know that the "terms and contions" pages out there are constructed to be as obtuse and uninformative as possible to make users just skip them.