A duopoly or oligopoly isn't much better. There's still a marked lack of choice for the customer, which results in lock-in and higher prices.
The Hacker News readership includes many people capable of starting ISPs. Comcast's large profits, which have been used to fund a string of high cost acquisitions, are a juicy target for potential competitors. Yet you never see discussion of ISP startups on Hacker News because the barriers to entry protect the current carriers. This wasn't the case in the 90s, and had Hacker News existed back then ISP startups would have appeared frequently.
The issue of telecoms not having competition has been the case for years. Back in the BBS days Jack Rickard used to harp on this in Boardwatch [1] magazine. I recall him saying something like, "Two guys with a screwdriver should be able to start a phone company."