Humans have weaknesses that can be abused. This is clearly the case in gambling. The government must protect in some areas. For example with financial advice, there are countless cases of people giving inappropriate financial advice to the elderly, even getting them to sign away their property while dying in hospitals. Sure it easy to say 'and gasp let people do what they want with their property'. But what about this scenario? Would you be OK if that was your relatives being manipulated on their deathbed to give money to a previous stranger cause it is what they want to do with their property at that moment in their life. Or, back to gambling, is it fair on the children of the father/mother who gamble away their pay check each month leaving the family destitute?

Above is more extreme but real examples to clarify a point. In my mind saying people can do what they want with their property is overly simplistic and assumes a more perfect world than the reality.