Ok, suddenly the casino you're playing asks you for proof of income to be able to withdraw your winnings and to keep your account in good standing, your bankroll every month is $500 and you provide proof of salary that you are making $500 net every month, will they accept that proof will they accept that you are putting all your salary for gambling, will this violate the principle of gamble for fun, because you are working to gamble based on your proof income.
First this is a very crazy scenario which can only happen 1) in the movies 2) if the government decides to take over the casino business. But then again it would be a terrible business model. Now let us assume that this is the case and everybody is okay with it, it will not violate the principle of gambling for fun because using all of your salary for gambling is the extreme of gambling problem/ addiction.