To be frank, if people/corporations/businesses/etc had not proven to be selfish and only out for money throughout most of history, we would have a market that would literally be free (Laissez Faire capitalism). And if such a world existed, where every individual could be trusted to do the right thing, have ethics, it would probably work. Now correct me if I'm wrong, but I have the sneaking suspicion that we actually don't live in such a world.
While I certainly agree with what you're saying, things are a bit more complex than that. It's illustrated with a known experiment of which I unfortunately don't know the name. It goes as follows...
Let's say we have two people (A and B) and 100$. Person A has to divide this 100$ into two stacks: one for himself, the other for B. The stacks don't have to be equal in any way. B then has the choice: either he accepts the way A has divided the stack and they both get the money...or he refuses, and they both get nothing.
Now...put yourself in the shoes of A, and then B. How would you divide it? Which amount would you accept?
The free marketing school of thought would let you believe that A will always give himself 99$ and only 1$ to B, and that B would be willing to accept that because 1$ is still more than 0$. However...this sort of logic simply does not work. It's been repeated in different countries and cultures, and time and time again, A mostly goes for 50-50 to something like 60-40 in his favor (there was even some tribe where A donated MORE to B than half the money). Anything more and B will refuse the offer.
The conclusion: human beings, on average, aren't self centered egoistic bastards. Seen in that light, regulations for things like e.g. net neutrality wouldn't be needed. Since people aren't, by nature, egoistic, why would companies (who, in the end, consist of decisions made by people) do it?
That reason...I think it's not yet clearly investigated enough to pinpoint the main reason, but there is more than enough evidence that the above simply does not work for companies*. It may be peer pressure in the board room, the fear of making a loss, the lack of personal contact with the 'B'-group or any other number of reasons, but the end result remains the same: under current market laws, ISP's WILL attempt to squeeze every dollar out of their costumers. They WILL use an unregulated internet to regulate it in the way it'll profit them the most.
The scariest part is even that they probably won't even realize what they're doing. One of the documentaries I rewatch from time to time is 'Enron: the smartest guys in the room'. I still have a hard time believing how they purposefully caused electricity blackouts to reap the profits of the "scarcity" of electricity, and at the same time believed they were doing the right thing (at that time, that is).
*and incidentally: the group where the 'A'-group of people showed the most greed and proposed 80 or even 90$ on their end...where freshly graduated economists. So yeah...guys like Gordon Gekko HAVE inspired people into thinking that 'Greed is good'.