Having spent many years in corporate America, I believe I've become somewhat decent in spotting the things that will eventually get shot down. Almost every time a company offers "free, unlimited, included, etc" plans or benefits, there is almost certainly someone looking to take advantage and/or share it with others. Everyone seems to have a great case as to why their membership is able to be able to be shared as they please. The business doesn't always agree. Changes don't necessarily start with widespread fraud that is a significant portion of the userbase. It is usually a small percentage that ruin it for everybody.

The AU business for personal is mostly targeted around keeping the family engaged with the model of the product. For businesses, same thing, but for employees. Driving that big spend. By some of your definitions, AMEX would be happy if people sold access to be an AU for a small fee (for personal gain). Because AMEX is collecting more AUs, right? They likely anticipate that this decision will drive more AU fees. If I held the card, of course I would get one for my SO, if it made sense for us. It's silly to think that this will become the wild west because the universe centers around collecting AUs.