Most people in my place will say gambling is a sin. Why? In most cases, gambling will lead people to a bunch of bad things. First, with gambling people can ruin his life and his family due to the end result for most gambling activities is a lose. Second, with gambling people can be very lazy. They tend to forget their responsibility in the real life(jobless). And still much more bad effects caused by gambling.
But, for some people that able to manage their time and money, this activity can give them a good entertainment.
If you are referring to a sin it should be the law of God for everybody and making a statement that most people are not getting benefits in gambling is not equivalent to all, so that is not a sin. It is just those people who are not getting good results are not seeing what gambling is supposed to be for.
I think if we discuss this will not be done, due basically to belief each, like @emberbekas said gambling actually have bad side, if you know over 75% people lose in gambling, but back it to individual self, it's actually a choice. I personally sometimes gamble, not using my amount, i'm using from bounty to make a bet because i can't afford to lose my money, yes bounty is have rules which i need to effort to earn it, but i can afford to lose using it.
