Many people have tried this in the past and also with many different exchanges and services.
Basically if you make a new account, deposit BTC, and right after you withdraw that exact BTC, your account will get locked.
Exchanges/Services have to do this to prevent their service from being used as a "mixer".
But how suppose they can withdraw it directly without completing their 2x wagering amount? I do not even think that anyone want to use FJ as mixer while they need to risk their chance to win some amount. If the result is profit then they get nothing to lose, but I do not find that it will be easy if you losing it, since it is gambling site who can predict the result?
This will be never ending debate IMO, the requirement does not really matter for some players as proven with the number of their active players but it might be a big problem for some other players. In my opinion the best solution is "take it or leave it", any sites has their own right to make their rules, players has their own right to accept it or decline it. So if we do not like the term then just leave it but if we are OK with the terms then we may go on. I'm trying to be neutral here, not supporting both side who are pro with the term and who are against the term.
I am just telling you guys how I feel about FJ being a mixer, this is ridiculous if they make it that way because what I know FJ is better on gambling not became a whatever mixer as they say. Like you said if they accept then take it and if they do not, leave it. But what I say before about the risk taking, it is just feeling absurd if people have their money but still want to risk it just to mix it