My home PC is an integral part of me accessing the Internet, just as the backbone is. If a company wants to be a dick about it, let them; we can just use another company, or let one form in the void left by the dickish one. This applies regardless of the component: my PC, electricity, hard drives, networking gear, last-mile providers, backbone providers, whatever.
In a ideal free market that is exactly how it should work. Consumer choices, based on previous corporate behavior, should help determine future corporate behavior.. essentially telling them how you view their company and their competitors by where you spend your money. However, what happens when there is no competition (there are plenty of places with only one last-mile provider for broadband). What if the local government made a deal with a single broadband provider to hike up taxes to discourage potential future startups and established competition moving in. City governments have been known to do this as a trade off to get a single broadband last-mile provider to even consider providing service to their city. It's great for the short term for the city and it's residents but in the long term it's very prohibitive for any competition to establish in the area. What happens if there are two service providers in the area but they are colluding? Unless you're living in a very large city area I suspect you'll have problems finding more than two broadband providers that will service your area.
These situations can and do occur.
I don't see anything magical about any part of it. If a company wants to build backbone access and sell it, fine. If they want to stop, fine. If the market is open, other companies will fill the void, because there's untapped profit if some other company just closed shop. Putting restrictions on the market can only make it less efficient, less-able to deliver the best solution.
Again, you're assuming the companies are playing by the rules. There may be a market as far as people who'd be willing to switch providers to a new one but other situations in the area may still make it not profitable to do business there. As I mentioned earlier it's entirely possible for the established provider to have tax breaks and other incentives that new competition wouldn't have and some of these can be bad enough to overcome even a very large potential subscriber base. Then there are all of the political issues to get through like right-of-ways and pole rights for running fiber. An established provider is going to do anything in their power to make new competition in the area as difficult as possible.. it's in their best interests to do so.
If it did that, it would be leaving an opening for another power company to deliver power more cheaply. If not, then the overcharge is small, or there aren't very many families with more than 2 people. Why should the power company not be able to charge whatever it wants? (again, assuming it acquired all its property via voluntary exchange). After all, nobody else is providing power to these people. Why should the company that decided to do so have dictated how it will run its business? Surely it's not illegal for it to just close up shop and go out of business, yet that would leave everyone without power. Maybe I'm missing something here, I just don't get the logic.
Again, it can be incredibly difficult for new service based companies to move into an area especially when there is infrastructure to build. An existing power company is not going to let another power company use their poles and why should they? It's possible the existing power company didn't even have to entirely pay for the infrastructure to begin with.. there could have been grants or other government funding involved. The only incentive a company with no competition has to keep their prices somewhat fair is that they know that there is a breaking point where the consumers will no longer pay for their services, even something as basic as electricity. However, that won't stop them from getting away with as much as they think is possible before it will start to seriously effect their bottom line.
Keep in mind also that the infrastructure costs you mentioned earlier in regards to the broadband providers didn't necessarily all come out of their money. From what I understand, in the mid-90s the telco companies were provided a LOT of money in tax incentives to build a more robust network and even fiber to the home. That never happened and yet they still took the money. (Can anyone fill in more details on this? The only thing I could find was $200 Billion Broadband Scandal)
