The book gave Wal-Mart as an example, and said you can make more of a difference, even if you still shop at Wal-Mart, just buy contacting the company and telling them you don’t than by not shopping there, but not letting them know you are doing so.
This brings up an important point about the Keeper (or any "alternative" menstrual product, really). They can't really advertise effectively, and word-of-mouth is a powerful tool for these companies (especially with the way many of us sing the praises of our cups to anyone who will listen). How many of us found cups because we heard someone else (either in person or online) talking about them? Even the stickers we may have seen in the bathrooms were put there by a cup lover spreadin' the word. Now how many discovered them on our own (tv adds, radio adds..)? Probably not many.
This gives us a bit more power in this situation than we would have against a company like Wal-Mart or KFC. Even people who use and love Keeper products can help the effort (if they so choose), by writing to the company telling them they aren't going to support the Keeper or Moon Cup (US). Saying you read about the problem on an on-line menstrual cup community will also let them know that many others are seeing it. If we have any power as consumers, it would be in a situation like this.
Just a suggestion.