In the Talmud, the rabbis take a dim view about gambling. Besides being a risky enterprise financially, and addictive, the rabbis say that the winner is really a loser. Morally speaking that is. How so? Because the fellow with the inferior hand wasn't expecting to lose. Therefore, the loser relinquishes his money reluctantly—it's being taken from him willy-nilly, and he is getting nothing tangible in return. In simple English, it's a bit like stealing.
That's not all, though. Gambling, whether betting on horses, roulette or cards, only gives the illusion of contributing to the local economy. In the end, though, it contributes nothing of value that endures.
Rabbi Eliezer Danzinger for Chabad.org