Anything done moderately cannot cause any harm or negative effects. Everything has a good and bad side but it all depends on what you allow to take over. Things like gambling, drinking, smoking and even something that's non harmful like eating can be harmful when they are done without discipline. Gambling can be a source of entertainment and it can also be something very disastrous If you don't do it responsibly.
When gambling is considered bad and has serious effects on someone, it means the person is not doing things right; I mean applying discipline, wisdom, and understanding to gambling. When gambling is done in the proper way, there is no negative effect to be seen. I place all the blame on ignorance because it is the reason why gamblers are negatively affected. If there is an understanding of gambling as a game that is unpredictable, and that winning occurs as a result of luck, I'm sure gamblers won't be negatively affected. However, they go into gambling without a better understanding.