I see the discussions in this thread largely focus on profits, but I believe there's a different main reason why gambling should be legal. I think that it's a simple and reasonable idea that an adult should be allowed to do whatever they want to themselves, as long as this doesn't harm others. So legalizing gambling is an easy yes for me (gambling is legal in my country, by the way, and was very abundant even when it wasn't legal). There's addiction, but it's not more common than alcohol addiction, and yet alcohol is usually legal. I would, however, make some strict regulations for both alcohol and gambling, when it can pose a threat to others. So, for instance, I think that people who are legal guardians of children under 18 should be obliged not to use the minimum amount of money necessary for food, shelter and medication of them and their children for gambling or alcohol because this can lead to very harmful consequences for others. But enforcing such rules may prove to be difficult.
Quite right. Talking about the profitability of something while forgetting about the principles is a very slippery slope that will not lead to anything good. Violating the freedom of people is in any case a bad idea, even if such a desire arises from good intentions, we have seen this in history many times.