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.