For Comcast and all other cable operators, the issue is network stability. Why should a neighborhood of 100 (or 1,000) Comcast customers be at the mercy of one customer who decides to turn on three or four computers in his home and start a massive peer-to-peer file-sharing download?
The cable company needs to be able to throttle back certain kinds of traffic in order to keep a small number of customers from negatively impacting performance for a large number of customers.
Networks are built on average loads, not peak loads, like the electric company, the gas company or the water company. If network operators cannot regulate a handful of abusive customers, who saturate their network at certain times of the day, they cannot guarantee any of their customers reliable service at any time of the day.
The cable provider's ability to control how many hours of porn you download (or even which porn you download -- or which TV station you watch) is a peripheral issue because demand will drive which services you can access.
The threat is not that Comcast has the technical ability to do that. The threat is that the Patriot Act permits the U.S. government to ask them to do that without presenting them a warrant served in a public court. And even worse, legislation protects them from being sued even if the government action is illegal and the network provider complies anyway.
There is simply too much money to be made for Comcast, or anyone else, to care what you do with their service, as long as your use of their service is not detrimental to others who also expect a certain level of service from the same provider.
Thanks for the opportunity to comment.