It can only become wrong when you're abusing gambling. When you're getting addicted and gamble on a regular basis, it becomes wrong. I think that if you gamble in moderation it will be okay to gamble every now and then.
You should never lose more than that you're winning.
Yeah people without self control keep on playing and abuse the gambling system. This way they end up with big losses.
If you are real about it, it isn't the gambling which is doing something wrong, but more the person gambling..
The best gamblers always know when to stop. I think if I was rich I would do very big gambles but very rarely, like a couple of times a year just to test my luck, other than that i would never bother, it's not that exciting once you have the money apparently, all those rich people aren't gambling addicts usually, they do it in a casual way.