How much would you be willing to pay for just the channels you want to watch? Lets say a local cable company to you carries the History channel and that cable company pays a $100 dollars a month to carry that channel. If you are the only one watching it your saing your willing to pay $100 for just that channel? NO? Well then you must think that every one else who has cable should subsidise the cost of that channel so you could watch it? This may seem like a silly comparison, but thats how channels are aquired by a cable provider. They pay a price for a channel or group of channels sometimes dependant on the number of viewers sometimes a set price. The cable company cannot absorb this whole cost, it would still just drive up rates for everyone overall. Cable companies have risked dropping channels before in order to avoid paying channel providers a higher fee for the content. Charter just earlier this year almost lost a whole series of channels from (Viacom?) in order to prevent a rate increase.
In order to go to a true a la carte system, two thing would have to happen. 1) the Cable provider would have to be an all digital system. Which would require a box for every tv. You cant use a series of filters stacked up on each other to chop out the channels. Too much signal degradation would occour. What if a sub only wanted 5 channels, how many filters are you going to stack up to make that happen. With a box, you could just teir mask the device to authorize certain channels.
2) Instead of going after the service providers ( Comcast, Dish, verizon) the focus should be the content providers. Force them to provide the channels a an a la carte price as apposed to a set price based on the number of subscribers in a system. Make ESPN charge the service provides say 1.25 or so per month for every person that actually wants to view it.
A la carte while feasable is not going to just happen with out driving up costs for someone and that tyipcally going to be the one who only wants a few channels