Gambling can be an addictive activity, as it is "exciting" to play with risk. Some people are addicted to the adrenaline rush of risk.
Any organized gambling is automatically a losing proposition, since the organizer will have to take a cut, so the odds are automatically against the player.
Legalizing gambling is up to the government to decide. The government basically must weigh the benefits (taxes, ancillary business, organized nature makes the whole thing easier to manage), vs. the costs (human toll such as increased crime, gambling addiction, etc.)