American consumers aren't dumb
Your several arguments are quite weak, and the court's ruling does have some strong points. We can only hope that, by putting the regulatory body on firm ground, we can get regulations that everyone abides by.
First, a duopoly isn't a wide open market, and the real feet-on-the-ground experience of American internet users is clear : there's rarely a reasonable choice. The court reasons - correctly - that the duopoly power we've created in internet service might be better than a pure monopoly, but it isn't a free market. Your statments that a customer "would just switch" are simply laughable to most of America.
In my area, I can get service from Comcast/Xfinity, and from ATT/Uverse. Right now, Xfinity is providing much better quality of service - my Uverse friends say they have multiple outages per day, periods when ATT's core routers seem congested and broken, and switching to Xfinity cleared it up. In my area, Xfinity offers speeds to 150Mb/sec, Uverse offers 20Mb/sec. Wireless in my area is possible (10Mb/sec), but cells seems to get jammed up now and then, hard to keep a VPN connection live - and wireless data fees are high (roughly $10/GB).
This is, at least, the duopoly at work. Many people I talk to are living with Uverse's poor service, but some are switching. Some stick because of the visceral loathing of Comcast, some can't be bothered.
If we add another axis, where each provider blocks some set of websites, good luck to me for figuring out who I'm going to use as a provider. One partners with Amazon, one with Netflix. What, I'm supposed to get both turned on? The court argues this is ridiculous, that limited set of provicers is reasonable for physical infrastructure, and thus is rightfully regulated.
Finally, we - internet users of america - aren't worried so much about blocking of a single media website like Netflix. Your straw man paints an unreasonable light. The real fear is google being held up to ensure quick response, and every other media company. The Reg certainly has a dog in this fight - they might be required to wrap their content in a larger company's livery (imagine: Yahoo), pay that company for the privilege, that company is paying off the ISPs for reasonable carriage, and The Reg has to squeeze all its contributors.
A poor way to run a railroad.
Leave the duopoly as it stands, but require "common carriage" style rules, allowing these companies to compete in a marketplace without a torture of 'if I want this movie series I have to choose that ISP'. That'll be fine.