I don't think defrauded is the right term since banks/lenders know that being an AU boosts credit scores without the obligation. Diligent financial underwriters that look at more than just the credit score can see this and discount it if they decide to do so.
Do you see how ridiculous that sounds? "banks should allow me to add stranger AU's because the underwriters should know better". Yeah...no.
I read meatgrinder's post as saying "defrauded" isn't the best word, and I would agree. The determination to count AUs for credit purposes even though there is no obligation was made by the financial industry. That isn't to say that they must allow this; merely that operating within their rules is hardly fraud.
For example, some ways that the financial industry could react to close down tradelines on a broader basis, rather than an individual account, are:
-Counting the AUs credit only for the duration they have been an AU, not the full age of the account (a la AMEX)
-Count AUs but only for a fraction (1/10, or 1/100) of the total limit
-Put in their TOS that AUs must have a verifiable relationship with the account owner of personal CCs in order to be added. This would preserve AUs counting for spouses, etc.
-Don't count AUs at all
I'm an underwriter (insurance, not banking, though). Underwriting for personal accounts is almost entirely automated in every sector that I know of; not just because of the processing time and money but also because of the regulations that personal financial services are required to meet.
If my company told your state that we would write your insurance for $X if your credit score was Y, I am required by that filing to offer you that $X premium even if I knew for 100% that your score was artificially inflated. (And in practicality, I would have no way of knowing that. Credit score calculations are so inscrutable that almost any score could be associated with any individual's other data.) If I failed to do so, my company would be subject to fines and penalties for not adhering to what we said we'd do. We could argue that the score was artificially manipulated, and we would be told "You should have thought about that before you decided you wanted to include it in your rating. Sorry not sorry."
As an analogy, you know how most insurance policies provide for a "good student discount" where A- or B-average grades reduce the amounts you pay for insurance for that student? Insurance companies know that there's a wide variety in "B-average" (kids who are taking AP/honors classes versus kids whose parents told them to schedule a bunch of fluff classes for the term prior to getting their license to bring up their normal D-average). They know the system can be gamed and even within that variety and with that gaming, it still makes sense to differentiate student drivers on grades overall.