You are a jerk for calling them jerks. If it is "pay what you want" then you are invited to do exactly that. If you want to pay nothing, you may do so. It is perfectly inside the rules of the event.
In certain designated areas of life, such as during a boxing match, the rules are different: if you're in a boxing match, you can indeed punch someone, and you won't get thrown in jail or suffer any other sanction (other than being punched back). A boxer who punches his opponent in a boxing match is not a jerk, because that is permitted by mutually agreed upon rules in that context.
In the case of the cards, the rules do explicitly allow paying $0, so it's in no sense a perversion of the rules, and people who paid $0 are not jerks.
"The rules" don't define whether you are a jerk or not. How you behave in the situation, does. They said up front that it cost them $3 to give you the cards. If you paid $0, you knowingly gave them the shaft. That's jerky.
This reminds me of http://www.untoldentertainment.com/blog/2011/03/05/holding-t...
The wording also said there was a suggested price of $5. "Pay what you want" is the equivalent of saying "tip what you want". You could "game" an open bar by never tipping, but that would make you a huge jerk.
Society is not based on rules. It is based on social interaction. You can break the rules and not be a jerk, and you can follow the rules and be a jerk. Rules have nothing to do with jerkitude.
Oh, and if I told someone "take as many potato skins as you want" with a bunch of other people there who might also like potato skins, and you take them all, you are again a huge jerk. Being nice to other people is important. Just like you shouldn't take all the potato skins, you should try to reimburse the makers of the game for at least their cost.
I invite you to score yourself in the psychopathy checklist (http://en.wikipedia.org/wiki/Hare_Psychopathy_Checklist) and let us know how it went.
Why are you so angry over this? Perhaps you should seek help.
Rules were established. Transactions were carried out according to those rules. Shock, horror, your supposed victim even made a profit (according to their own accounting). Why are you angry?
Everyone who bought the cards for under $3 was faced with a decision: do I want these badly enough to literally cost the people who make them money?
Did you answer yes? Cool, you probably acted selfishly. Own it.