I don't think you ARE ALL as innocent as you make out ...
Never downloaded a 'second' program, where you've only paid for one? Never ( somehow ) viewed something online - where you 'should' have paid for it? Never used a valid train ticket you found, just before you needed to buy one? Never picked up a coin or note from the street, and kept it? Never read the paper you found on your train seat - because YOU DIDN'T PAY FOR IT !!!!
Come on ...
This isn't about what's been paid for, or deemingly 'stolen' etc.
This is about clicking a button on a computer !!!
I've often 'tried out' things online - just to see what will happen. ( except paying for certain types of credit card downloaded material )
My position on the matter is, and will be, that if the system allowed me to do it - then it's not 'all' my fault. I DID NOT click onto any type of 'agreement' prior to entering the promo concerned, to say I would agree to enter ONLY ONCE.
A kitchen knife is used to assist in cutting work when cooking, primarily. AFAICT most knives don't come with an instruction manual on how you should use it or cautions in using one. If you hurt yourself, is it the knife manufacturer's fault? After all, they had no warnings, they didn't even tell you "here is the sharp part of the knife", and nothing on the knife is designed to stop you from hurting yourself (accidentally or deliberately). The "system" allows you to do anything with that knife, but in the end no matter what happens, the consequences are
your responsibility.
I know that analogy may not necessarily align with what you're insinuating, but I'm not content with the way you are trying to allay a significant proportion of the blame away from yourself when, in my honest opinion, that blame is almost wholly deserved.
I don't think anyone is owed anything in terms of warnings or what not here. In fact, from AFF on the relevant thread for this promo, until recently it was never insinuated that this loophole could be exploited. So no one could really get this advantage scheme from AFF (except 2 days ago, when PC probably started to come around).
As for any other scheme, most here do their homework, their due diligence and....most importantly... their common sense check before heading into something unusual, irrespective of what gets initially reported. I thought most people did this for most activities, so warnings may be useful but they don't replace looking out for yourself! Especially when something appears to skirt on the edge of morality or legality.
Again, if you are that unhappy, please see FT to see if a class action or other kind of regulatory complaint is being arranged; consider your legal options. If you can prove that what you did was 'innocent' with no intent to defraud or get around the system, then you may get off the hook; that is, take the argument you have here and see if you can bring it forth in some legal environment.