Even if they get addicted to gambling, if they gamble with small bets then the impact on their lives will be less and they will have at least controlled the amount of money they play. If they can keep a balance at it they will entertain themselves by gambling.
Your right, no matter how much advice you give someone they will mostly just whatever they want in the end. A few people can be helped but the majority cannot, it is why so many people can't quit their drug addictions.
Its really only a problem when people go into debt and start selling off their personal assets such as their house and car. If they are only losing disposable income it is not a big deal.
We can advice or convince people to enjoy gambling nor quit it but you don't have the control on making a fixed decision on what they would do.