Why focus so much on individuals? Look at the countries where gambling is 100% legalized, such as Macau and Monaco. These countries have become super-rich due to the tax revenues from casinos. Also, huge number of jobs are created as a result of gambling.
Bad effects will occur and the impact will be greater than the good one. Not all countries can legalize gambling even though the potential state revenue that can be obtained from this sector is quite tempting.
It depends on what country we are living, gambling is just a form of entertainment but it's an expensive type.
Poor countries are against gambling because they know it will only make their people poorer as people are desperate to make instant money without knowing their chances.
They do know their chances. They know that they have really small chance of winning but the thing is, they don't know how little. In lottery (which is another form of gambling), it is said that your more likely to die on your way to buy a lottery ticket than you winning. Just imagine how little that chance is.
I think countries are banning gambling so that it will not be in the majority of people's minds. People wouldn't make it an option because they know it's illegal. Some people would argue that there will still be people gambling since there are still people doing drugs even when it's illegal. But as you can see, there are far less illegal drug users than drunkards because illegal things aren't our immediate coping mechanism since we know that we can go to jail for that which will pretty much make our whole life go to waste.