I think it makes sense because retail ISPs operate in a two-sided market. Comcast provides access to Internet services, which customers want and are willing to pay for. Similarly, Comcast provides access to customers, which the Internet companies who provide those services (and associated CDNs and transit providers) want and are willing to pay for.
I don't think there's anything especially wrong with this business model. It's similar to how a newspaper charges both readers and advertisers for access. The disadvantage is that you have to keep both parties happy.
Incidentally, if customers uploaded the same amount of data as the Internet services, Comcast wouldn't get transit fees but it would get additional revenue from the customers, so I think things would balance out.
I don't think there's anything especially wrong with this business model. It's similar to how a newspaper charges both readers and advertisers for access. The disadvantage is that you have to keep both parties happy.
Incidentally, if customers uploaded the same amount of data as the Internet services, Comcast wouldn't get transit fees but it would get additional revenue from the customers, so I think things would balance out.