One problem with the "impersonation" argument against Comcast's behaviour is that many ISPs impersonates services to some extent.

A common one is to redirect port 80 requests to their proxy server so they can cache pages, reducing use of their internet links and providing better service to their users.

Another is redirecting SMTP connections to their server, so they can monitor the traffic (and potentially cut off spammers). This one is a bit more controversial, and is a pain if you are trying to access a corporate SMTP server while on the road.

Now I realise that these two examples are quite different to inserting TCP reset packets into an overwise untouched stream, but it makes arguments like "the ISP should never interfere with customer TCP connections" a bit less clear cut.