With regard to Amazon's Visa CC ban. Personally, I think it is good. The banks have been leveraging everything they can with little regards for customers. Amazon is also a customer, and like the rest of us have had enough. For years now many small traders have refused to accept credit cards because of high fees. Now one of the big players (Amazon) has stepped up to the plate. It will also have an impact on Amazon, but I suspect that bank customers will start asking for an alternate CC like Mastercard, or start looking for a new bank, because using Visa is inconvenient.
In the short to medium term, I would not be surprised if companies like Walmart and Tesco also do the same, when and if it becomes clear that Visa are getting worried and are showing signs of buckling..
In the longer term, I would expect that Visa will be forced into line with the rest of the market. Not a day too soon as far as I am concerned.