Is gambling OK? Don't bet it! There's not an easy or instantly obvious proof text answer to that question.
In my own opinion, gambling is not a sin if you are just playing gambling for only entertainment or fun, but if you take gambling as a scheme to earn profit it is a sin because you will get greedy in playing and you might lose all of your money in gambling that amy ruin your life.
In that regard it doesn't matter whether you win or lose. Thinking all the time about earthly things, like making money with gambling for example, considered sin by most religions.
And you said it right about gambling for entertainment purposes. Since it's for fun only it can't be a sin, no one forbids to have some fun from time to time. That's just my opinion, of course, I know some religious people wouldn't agree with me.
- In the social aspect, people who do not know about gambling and they follow the religion, they always think gambling is a very serious sin because gambling is the place where greed becomes the most powerful, then this greed will destroy ourselves, our family and our society, it's just the place of the lazy, do not want to do but still want money, this is a bad behavior and should be criticized. However, in our minds, modern people, we always think gambling is just entertainment, if we do not affect anyone, we will not need to feel it is a sin, this is something I think is very accurate, each one has its own religion, we can not criticize others, right and wrong are dependent on each person, we can not force others to hear our opinions. We only live once, we should do what we like, do not care about the comments of others