Comcast also considers themselves a backbone provider even though they are in the business of delivering content. Level 3 is paying for access: they pay in the form of "peering" peer access. On another level the problem is the idea that Comcast should decide these issues. Part of net neutrality would be clearly laying out the rules for this sort of thing. There is an old saying among lawyers that hard cases make for bad law. This is an attempt to set a precedent that could lead to Comcast streaming Democracy Now videos in grainy jerky, slow form, while streaming CNN videos smoothly and clearly. The internet has never been the pure free speech zone some claim. But legitimately it is an arena where very small players can deliver the same or higher quality than the big boys, and make that content as accessible as the content of the big boys and try to compete on that basis. (The big boys still have huge advantages, but being able to deliver quality and content and comparable to theirs or better and be able to distribute it still adds to democracy and diversity.)
The precedent here would be chilling. My bit about how life wasn't fair. Of course a shorthand, as that cliche always is. Here is the long version: We need rules to ensure that backbone providers and ISPs can't discriminate on the basis of content. At the same time we have to provide protection against free riders. If the way we balace that is to provide great protection against free riders, that we leave huge loopholes for discriminating on the basis of content. If we have strong rules against discrimination on the basis of content then there will be loopholes that free riders could use. A perfect balance would be optimal but also impossible. Regulation is by definition "one size fits all" (or at at least a limited size selection). So given that loopholes will exist one way or another, I think free speech is tremendously more important than making sure multi-billion dollar companies never have to deal with free. Strong net neutrality regulations to protect free speech and diversity of opinion are critical, even if they result in loopholes through which a certain amount of free riding take place. And again it is not as though Comcast does not have alternatives to limit such free riding. If they think the can't really afford the bandwidth they provide they can lower the maximum bandwidth again though that may be the final straw that leads their customers to rebel. Or if the problem is not total bandwidth but peak bandwidth, they could put in dynamic bandwidth usage depending on what other customers were using encourage stuff that is not time sensitive like certain types of downloads to move to "off-peak". Or they could take the money they are using to buy NBC and freaking invest it to increase their capacity, instead of complaining when customers actually try to use the bandwidth they are given in their contracts.