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.