If Gambling is for fun then its not wrong but if just spend all your money in gambling like a crazy then it is wrong as it will make you loose everything.
When you really lose everything youve got then you are doing it wrong,many people do it for fun and when they profit its enough for them.
When you win it is good, but when you lose it's wrong. This is how many people think.
And yes this mentality is wrong. The game is for entertainment and this should be it's main focus. Nothing more nothing less.
This is the right thinking but still many justify gambling by the profit. If they win, gambling is good but they do not see the negative effect of gambling. They will continue this kind of thinking until they are addicted to it and get into situations that is hard to get out like gambling debts and the likes.