Have you ever done the courteous thing when crossing an intersection, and waited back at your stop line because the lane opposite was backed up? Have you ever had someone making a right turn slip in while you were going out of your way to not block the intersection?
As Silicon Valley grew, people started moving into cities farther afield (indeed, they used to be fields), and commute in. The local city into which they move charges developers for extension of local infrastructure like water, sewer, roads, but there is no model to share that revenue with cities through which the new residents will drive to get to work. So the roads in the middle aren't expanded, and commute times for those who live nearer the jobs go as distant commuters clog the highways.
If I could construct cars for free, gas was free, and I had an infinitely large parking lot at my house, I could push cars out my driveway in a steady stream. Where would they go? And why should I not to this? After all, I've paid real estate taxes for my driveway.
There's been a fair amount of tearing-out-of-hair lately over the desire of BellSouth et al to create a throttling mechanism for the internet, in essence, to charge for bandwidth based on quality of service (QoS) metrics.
I frankly think that tiering only makes sense.
First, it closely models the real world. In the real world, I can choose between a free road which may be congested, and a turnpike which may get me to my desitnation faster. There are toll booths on the turnpike to both encourage the quality difference, and to charge me for the privilege. Similarly, there are car pool lanes, and fastpass lanes, all rewarding drivers who contribute some (arguable) value to the system with shorter wait times.
Second, much more than in the real world. traffic generation is very very inexpensive in the electronic. If all the T1s to all the content providers were saturated, the trunks would need to be much much much bigger, as would the switches that route between the trunks and access lines. Some might argue that the content generators already pay for their content to get onto the highway, but like me with my driveway, the physical limits of the driveway permit far more traffic than the system can accept in aggregate.
Now we might argue that this implies a massive increase of scale is necessary for the central infrastructure of the net. Probably so. But until this the scale is increased there will be those who take advantage of the current system and inject more traffic than their share, like the friendly gent who cut me off by making a right turn on red yesterday while I was waiting for traffic to clear. And the folks who run the roads will try to find ways (like "no turn on red" signs) to penalize that gent.
In the physical world, the different QoS metrics that exist for physical delivery of envelopes has led to a two-tier system of the government post office and private couriers. In fact it is multi-tier, as the couriers and post office eash have multiple levels of service at different price points. So my letter than absolutely must be received by tomorrow, will be received by tomorrow, for a premium carriage fee. Any amount of bulk mail can be pushed into the system by advertisers and not impact my letter at all.
What is so wrong about a tiered approach to net traffic? Don't we want content we've purchased to arrive faster than spam?