I don't think people are worried about the NSA breaking into their house or faking their identity, nor do I think anyone is concerned that the NSA will hear them talking about how they have been diagnosed with cancer.
I think people are worried that they will say something well within their first amendment rights on a seemingly private channel, that will then get them marked as a "dissenter" of some kind.
It doesn't have to be the NSA that breaks into your house. It could be an outside analyst selling information to a guy who knows a guy etc.
I don't think anyone, be it government or corporate, should be capturing and storing detailed data like this for extended periods of time. It's just asking for trouble. I haven't seen any proof of a worse case scenario more severe than ads being a bit less targeted if strict limits were placed on data retention and identification.
To reiterate your point, there has to be a strong chain of authority for the life f the storage. And they probably would completely replace 3 racks of storage with 1 every 3 years given increasing drive density. So that would be a lot of opportunity for a contractor to bolster their income by selling drives off on ebay.
I think people are worried that they will say something well within their first amendment rights on a seemingly private channel, that will then get them marked as a "dissenter" of some kind.