Is gambling OK? Don't bet it! There's not an easy or instantly obvious proof text answer to that question.
Maybe in religious belief gambling was a sin, but gambling didn't mention in the Bible. However, the love of money is the root of all evil which is mentioned in the bible. Where in my part of it I am 100% agreed and believed in the Bible.
People does not only gamble to win money or feed their greed. This depends on the purpose why people is going to Casino. If a person purpose is to have entertainment and enjoy himself then where is the sin on that. If you are using your own money from legit earnings, why would anyone consider it as a sin?