Back when I was a Comcast customer I did find it useful when I was in an area with no - or too slow - mobile-data connections.
I assume that traffic on that network is always qossed to lowest priority, but I've never used it (I don't use a BT router)
They never disabled my account - I not get worldwide FON roaming for free forever - yay!
I wouldn't want that kind of traffic flowing through my IP address, even if it was only for legal reasons.
If you are just a relay, the content is encrypted and your chances of liability are low. Same goes if you are promoted to a guard node.
How did the bank block you? By blocking your ip or your user account?
Cox is also very prone to turning off your internet at random times due to botnet traffic looking like it's originating from inside your network.
It's not just liability, for me it's also ethics. It gives me piece of mind that I am not contributing towards these practices.
Sometimes you have to look at the big picture when making ethical decisions.
Paying tax is mandatory, unlike installing a tor node on your modem.