If someone lose his money in gambling because of have fun, he already consider that losing money is the amount he can afford. He doesn't mind losing that money for fun in gambling because he just want to enjoy his time in gambling and no need to feel sad if he lose.
That is the risk of playing gambling and he know that so he just use some money he can afford to playing gambling and walk away from gambling.
That is not stupidity or deceit because he calculate everything before he gambling. If he lose, he will not bother to recover his losses because he know that is what happen in gambling.
Only if that's the real feeling of those gamblers who claimed to just gamble for fun.

The fact that these people who claimed only gamble for fun keep coming back, they want to chase a win. Continuous losing at gambling is not fun, and that's the reason why these people keep gambling.
Every time they lose, they will say they can afford to lose that amount, but keep coming back even when they are losing. Do we really think they are having fun with that kind of behaviour? Even millionaires and big whales who lose a large amount of money in gambling, and surely they can afford to lose that, are getting affected every time they lose.