Am I not understanding something here
Banning someone from your private establishment is within your rights. If they want to run their own business they can elsewhere.
Banning someone via an ISP is different because ISPs have so much infrastructure they can in some sense be considered a "public utility". Nothing would stop someone from advertising ritualistic kitten killing in a public park (except maybe indecency laws but those vary). Likening an ISP to a public park is more accurate. If someone posted a sign saying "no one convicted of smoking weed can walk through this area" you'd rightfully be accused of some civil rights violation in your park. Similarly, ISPs are a conduit no different than a park path.
Everyone chooses KF or whatever as an example of "bad people that should be stopped". That's great. No one disagrees. Anyone with more than a room temperature IQ sees where it goes though. Suddenly you won't be able to access things that don't conform to the government issued public opinion. Don't believe me? The Great Firewall is exactly the same technology.
It is legitimately not my problem, nor the ISPs, who is doing what on the big internet. We have existing laws. Use those to prosecute people posting kitten killing videos or whatever. We do not need to have ISPs using AI and shit as precognitiion to censor what they deem to be "unsafe speech" or whatever.
And this already happens all the time.
Maybe.
I don't think it's a problem if companies with extreme amounts of power have to give up some freedom of banning.
On a sliding scale though, you don't literally become a utility one day.
(And when it comes to "only commercial storefront space in a large area", I expect that to be very rare.)
This is actually very common in rural parts of the us fwiw. There places where the only grocery store is Walmart, and the only other place to shop is dollar general.
In this case there is likely a limit to what a private business can grow into before it wades into the territory of public utility. A tenuous but related situation can be seen in trademarks where Kleenex has actually run entire ad campaigns to make people call generic tissue "tissues".
There's a larger philosophical argument here. Theoretically speaking there should be no limits to private corporations. However, when your corporation becomes a stable of modern life and the conduit of major utilities of society all of the sudden things start to turn into shades of grey.