The simplest opt-in/out I think would be satisfactory would be to limit the amount of data they can associate with me to an arbitrary time period (six months sounds about right).
I think there has to be a price to pay from the data aggregator side if they want information associated with my 'real' identity.
Yes at a simple level you're right, but you could use the same argument about lots of things, for example I could opt-out of using the Internet but that should not give ISPs carte blanche with my personal data.
As to your question, I use FB fairly cautiously and I'd also rather not exclude myself from a social forum which friends prefer to use.
What I'm suggesting is a simple compromise, rather than give social networks an unlimited license to my data I'm happy to give them a more limited one.
I think there has to be a price to pay from the data aggregator side if they want information associated with my 'real' identity.