Most people that think of success with gambling or betting are just fooling. They will only know they are foolish after they have lost huge amount of money while some will become addicts and later know that they are stupid. Gamblers should always know that they can not succeed in gambling but be using small amount of money to gamble. But out of millions of people, the gambler can be lucky but a luck he should never think of but come unexpectedly.
You might have a point that you are making but it is harsh to call gamblers foolish and stupid. You could have found a more subtle means to relate your disapproval of gambling, an irony of the signature you are wearing.
I am not calling any gambler to be foolish but I am implying that what they do is foolish. Or if someone thinks he can make money from gambling and we all know how people are losing money but think he is special or more talented to make money from gambling, is that thinking not foolish? Or if he go for it and and start gambling because of that, is that not also foolish? Even if I have done it before, that means what I did was foolish.