This is not a solution and no country will agree to that. Test are too expensive and if that would be applied for casino visitors then many other businesses could request the same. Besides, like you've said, there is no guarantee that results are fully correct. Self discipline of people and to obey medical recommendations is the key but that is very hard to achieve.
And what is wrong is that each person decides whether to go to him in Las Vegas or not? Whether to risk my health when visiting a casino, I can decide for myself. In the end, mass protests in the United States did not lead to an increase in the number of cases by several orders of magnitude. Therefore, it is unlikely that a visit to the casino will significantly increase the number of patients with coronavirus.
Nobody really knows about it and if it proves there is no spread of the virus or an increase in cases, then why does this virus still exist while when there is activity in the crowd proves there is no visible increase in cases of the spread of the virus. After all, the new normal era is one step to restore the economy and with the new normal it is at least the casino can still operate by implementing the recommended health protocol and I think it can still be done and there is no need to do rapid and swab tests.