What is good about this strategy is that blockchain record can be shared globally, so the tagged address can also be blocked by other casinos, preventing the person to deepen its gambling addiction by preventing them from indulging in online gambling.
The idea is good and fantastic. The challenge will be the implementation. Which casino will implement it by their own volition by checking for gamblers who have been flagged on the Blockchain for addition? I don't think non will do that. Casinos are there to make money and if not for age restriction laws across different countries, they will allow underage to bet freely because they are there for the money not charity.
So, if the idea will be done that Blockchain can flag a gambler for addition maybe in a particular casino, the next casino can allow him to bet. But if that will be done and successfully, it has to be a law or legislation covering all casino to follow that restriction but if left open then it will lead to confusion and competition among casinos to win an addicted gambler to their casino where they are restricted in another casino.