Gambling for fun can be a choice for some players who have a strong self control. And also a hassle to players who may not be interested in winning big, but found themselves wrestling with losses. The technical thing with gaming is the emotional connection it has on players for money's sake. Demo mode would have been the best place for fun gamers, yet it doesn't resonates the thrills with genuine gambling.
With the demo we won't be able to get the real experience of gambling therefore I don't think we should be using demo mode. Demo mode are to be used for practice while we're still trying to get used to gambling. Putting in small amounts of money is the main way to enjoy the fun that we can get from gambling. There's good side to gambling but the bad side is more visible because of how people are gambling in an unreasonable way just because they're chasing after the money. You can enjoy gambling and still be making money therefore we shouldn't think we have to do only one and forget about the other.