It is an argument for de-prioritization. If you have blown past your 1T limit bu the rest of Comcast's network isn't too busy then it doesn't matter, but if the other people on your circuit want to use the data they get priority over your traffic.
It isn't. If you use a lot of traffic when the network is idle, there should be no penalty for this, because the capacity otherwise goes to waste.
If you use traffic when the network is congested, so is everyone else who is active when the network is congested, so you should all get an equal share if you're paying the same monthly fee, and a share proportional to your max connection speed if you're not. Nothing to do with how much you used when the network was idle.
