The problem is that, as they years went by and the capacity of the internet grew around them, consumers' bandwidth demands escalated. People now want to download 10s of gbs worth of games from digital retailers every month, and watch streamed high definition video at all times. If the average household would before average 500kbps on their 20mbps connection, suddenly they were averaging 5mbps, and ISPs like Comcast could no longer cope. They were in the unenviable situation of having to make their internet access plans several times more expensive and having to explain the situation to their customers (literally impossible; customers would flee en masse), or losing billions. Deploying their own network would take many years and be a very complex, very risky project. As pesky businesses like Netflix grew and became a noticeable portion of the amount of bandwidth running down Comcast's upstream faucet, there must have been talks about direct peering (large content providers, nowadays usually through content delivery networks, benefit from peering directly with large ISPs because they can then ensure their traffic flows as smoothly as possible to the end user). I imagine the conversation went a little like this:

Comcast: "Hey Netflix. It's important to your business that you are able to reach our customers right? Without us you'd go bankrupt. Pay us $<money> for the agreement because we're really starting to sweat around here."

Netflix: "Hi Comcast. Even though we generate a lot of traffic, our profit margins are low because we have a lot of licensing costs. Besides, that's not how the internet works. Your customers are the ones who want our goods. It's in order to access our services and others that your users even buy your services in the first place. They're paying you for it already. Without us you wouldn't have a business, because the free market would ensure that customers would get to us through a different company or route. We can't pay you $<money>."

Comcast: "Sorry, no $<money>, no deal."

Netflix: shrugs "Okay. That's too bad, but we'll just peer with your upstream providers such as Level3 and they'll deliver our traffic to your customers as usual, under the terms of your peering agreement with them. It will be a little slower but what can we do?"

Comcast: "Wait what? I thought the internet was like a truck, but it turns out it's more like a series of tubes?"

Comcast (which, let me stress, is merely an example here; this situation occurs with others as well), cannot extract $<money> from Level3 under the net neutrality model, because Level3 has a much more valuable network. If Level3 did not peer with Comcast, Comcast would not function, because Comcast users want to reach a lot of users and services elsewhere on the internet. Comcast might peer with someone else, but they'd always have to pay them, because the situation will always be the same: Comcast has the traffic demands of millions of users, but a relatively small amount of people outside Comcast actually want to send traffic to Comcast. Any other upstream peer will shove Netflix down Comcast's throat, because there is a single internet.

Without net neutrality (and I repeat, I'm talking about NN's actual meaning, not about the temporary US federal regulation that was in place for two years with the purported intent of protecting NN), Comcast can look at the traffic they are receiving from Level3, examine it and say: "Okay, customer, you can have these packets from Google but these packets from Netflix... Hmm, maybe later." This gives them leverage when negotiating with the likes of Netflix, protecting their business model (and, I'm sure, a lot of jobs they generate). They can pass this off as "free market friendly" because it's allowing ISPs to do whatever the hell they want. In that sense, it certainly is - it's free ISP market friendly. But what does it mean for the internet itself?

It means that, when a user pays for "internet" access from a commercial provider, they can no longer trust that to mean anything. If an end provider can make demands based on where traffic is coming from, and presumably block some of it, then from the customer's perspective all "internets" are different. The "Comcast internet", with no Netflix, would be different from the AT&T internet, the Verizon internet and so on, since the ISPs, who are free to do as they please, will provide distinct services from each other. Think about it. When one of the millions of users or companies connected to the internet someplace in the globe generates traffic, they have no easy way of knowing which networks that traffic will end up crossing. Before the moment a request is made and a server delivers a response packet/frame to a very specific IP address, the server did not know it was going to be doing that. When a small business puts content "on the internet", that content is available to every participant of the single, global internet who wants to ask for it.

These participants can be making the request through thousands of end-user ISPs. If a single of those ISPs could demand money for "traffic protection", so to speak, what's stopping all the others? Why wouldn't Deutsche Telekom AG follow suit and start asking businesses to pay them to ensure the business's traffic is delivered to german customers? What about Shaw? Talktalk? Telefónica? But if you're a small business, you can't afford to pay off all these people, so you have to pick and choose which target customers receive quality traffic from you, further eroding the fabric of the internet.

Proponents of your position have told me in the past that this is not a problem, because CDNs (or "cloud") providers have enough business volume to take care of paying everybody off, so a small business can put their website in the cloud and it will reach everybody, just like the old days. But centralization of control over the internet under a very small amount of cloud providers is already a problem, and that would only worsen it. If no business can make use of the internet without a middleman, the word "internet" loses its final shred of meaning. You can put your website up "on amazon" and it will reach <list of ISPs>. That's all.