It's not quite that simple. The GP post is correct that Cogent has a horrible reputation in the industry. Here's a synopsis of the most common Cogent dispute:
1) User in New York on ISP A requests data from Server in San Francisco on Cogent.
2) ISP A and Cogent interconnect in San Francisco and New York.
3) ISP A wants Cogent to carry the traffic to New York and drop it onto the ISP's network as close a possible to the customer (cold-potato routing), Cogent wants it off their network as soon as possible so they drop it onto the ISP A San Francisco interconnect (hot potato routing).
The question boils down to: which one of them is going to have to build a bigger national backbone to handle the extra traffic from the user in New York? Neither one wants to, and wants to force the other one to do it.
As to why ISPs are not blacklisting Cogent: they are. That's what all these bandwidth problems with Netflix are about: ISPs are playing chicken with Cogent, trying to force Cogent's customers to bully them into upgrading their network. ISPs aren't limiting Netflix: they're refusing to upgrade interconnects with Cogent until Cogent starts using cold-potato routing.
In this case, one of Cogent's customers blinked before Cogent did, and side-stepped the problem.