Wouldn't really call these "myths", more like just assumptions of the uninformed. It doesn't help though that gambling itself has a negative connotation to most people, hence why Myths 1,4,5 and 6 exist (imo), which is in itself a misconception since gambling is just like any other activity out there where you spend money to play. It isn't actually wrong to say that that is a myth in itself.
Myth 6: Having a gambling problem is just a case of being weak-willed, irresponsible, or unintelligent.
Fact: Gambling addictions can affect anyone of all backgrounds. Even people who used to be responsible and strong-willed are just as likely to develop a gambling addiction as anyone else, even people with higher educations or higher social status.
I actually wouldn't call it wrong, anyone who falls into addiction (or any gambling-related problem) can be simply called as irresponsible, and that's not wrong, but a fact that a person needs to accept so that they can change. It might be wrong to call/word it as Op said though, more like it should be "Only people that are weak-willed, irresponsible, etc can fall into gambling addiction".