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My question now is are there any moral, ethical or legal obligation to bar a person from gambling after physically observing that he is mentally unstable?
There is a saying, don't judge a book by its cover. so you see, what you see does not necessarily reflect what you actually think. so, remember that thinking like that is not true. personally, I have encountered many characteristics of people like what you said in this thread. although not in the exact situation and conditions as you say, I mean not like the case we are discussing. A person can style according to what he wants, even though he looks like he has mental problems. but we never know for sure, especially since the man acted like a normal person. unless you really know the person. in this thread, you say, the gambling shop claims that he is a regular customer and he has never behaved badly.
My question is, what should we debate with this person, isn't he/she has the right to what he/she wants? in fact, many people have mental disorders. even people like us who look neat, but have personality problems. many also have another side with mental problems, especially those related to gambling. IMO, referring to what you said, it seems there is no written obligation for the shop to ban it because of its appearance problem. on the contrary, your moral obligations will be questioned first, by welcoming them well and then asking about several things. if winning doesn't indicate a mental problem, why ban someone. physical appearance does not determine a person's identity, in fact we cannot judge based only on our eyes. the problem is different, if this man comes to a top casino which requires its customers to dress appropriately and in accordance with the regulations implemented by the casino. if it's just a gambling shop and the person is able and willing to risk his money, then that's his right. as long as it's not disturbing, as long as it doesn't violate the rules, everything is fine.