This argument doesn't make sense to me. The ISP's customers are using the ISP's network by downloading Internet content. The nature of the content should be irrelevant to the discussion. The ISP's customers are purely responsible for that usage, and it is part of - from what I understand - the service they are already paying for. The ISP's network is only "congested" if it is incapable of delivering on the service that was advertised (assuming for the sake of argument, some particular speed of access).
Thus, how can Cashman argue that "there is no model for monetizing the required investment?" Isn't that exactly what ISP customers are buying when they pay for access to the Internet through the ISP? The onus should morally be on the ISP to make a good-faith attempt to build sufficient connections to any content that's popular enough to saturate the links providing it.
Furthermore, why isn't it naturally the ISP's responsibility to price their access sufficient to cover current usage and expected growth in usage? New use-cases for the Internet are constantly going to appear. It is the ISP's responsibility to provide Internet access with sufficient throughput that it is not congested for any reasons under the ISP's control; and to price their access sufficient for investment to achieve the throughput.
"The latest BigMac hamburger caused hungry residents to swarm McDonalds and caused drive-through lines to be congested today in Cloudville. Gillis Cashman, managing partner at McPartners, Inc. says that, despite selling happy meals in record numbers, delays in drive-through lines will continue, since since there is "currently no model for McDonalds to monetize the required investment" to upgrade its drive-throughs.