This can't end well
This could only work if:
1) You are given a way to opt out so sharing does not impact your performance.
2) Comcast provides a clear audit trail over who using your access point downloaded kiddie porn.
3) Even if (2), Comcast needs to indemnify you so you are in no danger of being prosecuted for any misuse of "your" connection.
I have avoided Comcast to date due to their one-sided terms of service and this does not help.