The first people gamblers harm is their own family - long before any formal crime has been committed.
How can we regulate what a person does with their hard earned wages from their labor and precious time and then still claim that person has liberties of any kind? If you think about it, this is the one and only fundamental liberty that is foundational to all other liberties.
Even slaves get food and shelter as well as some freedom of movement and expression. What they don't get is to be able to buy what they want and own it.