How is that any different from allowing someone to pay more to use more of a plane (e.g. first class seats)? Is this just a general argument that everyone should pay the same and get the same?
The analogy of the planes is not very helpful, because each flight is paid for individually. The idea is that traffic to certain peers (not the ISP customers, but whoever they are communicating with) should not be discriminated against. So you can pay for faster service, but all packets coming from or to you would get flagged, not just those going to certain servers.
