What this will do is create a powerhouse negotiator with the content companies as they would represent about 1/3 of all cable households. Who really hates this deal is those content companies, and the satellite companies. If allowed, Comcast will have the power to negotiate substantially lower TV subscription costs than Direct/Dish, and take money out of the content producer/broadcasters coffers.
The other side is internet... but I'm not sure that this is going to affect their DSL/FIOS competitors that much. Maybe I'm wrong on this, but I think this is likely a secondary concern that lags behind the concerns of the networks/sat providers.