While I can appreciate your concerns over data firewalls as it relates to local government (privacy advocate, annual EFF donation, yada yada), I would like to see a real world example of it occurring in the US before I'd consider changing my stance on locally owned internet infra vs Comcast, Time Warner, et el (I will even put my money where my mouth is, and come after such a municipality personally with an attorney, that's the sort of thing I find fun).

If Billy Bob the municipal broadband administrator is “sharing his list of fags” with his hillbilly friends, you can FOIA logs, emails, records, and come after the city for their transgression. You can vote local government representatives out of office. If Comcast does this, you have no recourse (and they would even be within their right to sell this data to the highest bidder).