Gambling will only be wrong for the persons who are addicted to it. It surely wrong for them because there are many possibility on what they will end up if they won't stop or control them selves.
So blame those who addicted to gamble instead of blame the gambling itself. If they cant control themselves and get addicted, so it is absolutely their own fault.
Gambling is only wrong when you are addicted to it and dont know the right moment to stop because if you dont know that the chance will be high that you are losing a lot of money.
And that is bad because the money that you lost is all wasted and that must not happen you can better save it.