Off course gambling is wrong you dont have anything about it because on a long run the casino will always win of you but gamblers dont see that problem
and that is why they are addicted if you cant see that the casino is always winning you will stay addict for life.
It is not wrong to spend your money on casino. It is just a form of entertaining. You can spend your money on drinks, on gaming, on sports so why cant we spend on casino? It is only consider wrong if you start to ignore the others and make your gambling habit to hurt those close people to you.
You're right,
It will only be considered wrog if it does have contributes tothe negative effects to your life.
Whether it is Being a irresponsible socially, Being emotionally distressed or having a financial instability.
But still it depeds to a person on when he will take an action to consider gambling as a wrong doing for him/her.