that's right, especially if you just glance at the way they dress. of course it feels unethical. as long as he brings money and does not disturb other players I think it's okay to play gambling at the casino. especially if you see someone's character is different from one another.
Ideally, if the person is mentally disordered he or she should not go to casino and should not gamble, as he is not in the right frame of mind and therefore he can lose money when he is not fit to use his brain. If he insists on gambling, then it becomes the responsibility of his near and dear ones to stop him from gambling and the best way to do so is to restrict him from gaining access to the money. I assume that since he is a mentally disorder person, therefore we may not be in a position to do any job and earn money.
(If he is earning money through any means, it would mean that he is not a mentally retarded person).
Mental disordered people have different problems and not all of them won't be able to perform a job. Although in your last line Noormcs5, indeed, a mentally retarded person can't work and won't be in the gambling house. If he does should not be allowed by the families. The actions or moves to take wouldn't be same for each person. Only few humans are completely, 100%, mentally stable. Today's world consists of too many troubles that the newer generation may not adapt easily. In the sense that the person doesn't comply by the rules of the casino, can be pushed away in the casino. It'll be hard to detect a mentally disordered person than a retarded person. The later should be removed in the casino, as it's not conducive to have them around people who are working strides ahead to stabilize the mental health of themselves and their family.
Unlike people who are just depressed or mentally unstable, this has not yet reached state of insanity and people like this can still carry out various activities like normal people in general.
Only difference is temperament and emotional level, those who are mentally unstable or in depressed state really cannot be disturbed and they will tend to be alone.
If their personality used to be that of gambler, perhaps despite this condition they would still be able to gamble, it just that they would be relatively quiet.
I once found person like this in betting shop and it was very ridiculous because while he was in the betting shop he really avoided crowds and if someone else greeted him he looked gloomy or remained silent without word coming out of his mouth.
Most important thing is that as long as the people around you don't bother them then there won't be any problems because people like this won't show their emotions if they don't feel disturbed.
