The casino wins, obviously. If the government is smart they can make a fortune too: with fees and taxes on the casinos, plus taxes on hotel rooms and the crazy money some of the gamblers spend on conspicuous consumption. If you were limited to gamblers from your country I think it is a net loss. If you attract lots of people from other countries (which Singapore does) you get to siphon off their money into your country. And with that you can afford to spend a great deal dealing with some of the social problems caused and still make a great profit for the country.
I don't think it is the most honorable business. I think too many people are harmed. Plenty of people can just do it for fun (and they can afford their losses), I don't mind that. But lots of people lose what they can't afford to lose. Still, if you are paying most attention to the benefits to your country alone then casinos like those in Singapore can be very rewarding for the country. And money you make this way lets you avoid raising taxes (you take from the profits due to those willing to part with their money).