You're not wrong, in the sense that there are plenty of people who suffer from that "Just World" problem. But using it as a method to attack anyone who judges another at fault for failing to apply even the most basic thought to a a significant action does not require that you subscribe to the Just World hypothesis.
People who subscribe to that will blame another for what essentially constitute random accidents - a car hits yours when you had right of way - why didn't you do a defensive driving course? people are idiots you know!
However it's not the same thing to find fault with someone who, due to their own failure to apply common sense to a significant action, suffers loss (not the same as requiring common sense for an everyday action, attention is not always available).
It is also not the same to find fault with someone in the abstract, vs a particular person. Ie, to say that in general, those scammed by 911 mails should have known better, that the entire thing is both too dodgy and too good to be true, is not the same as berating your grandmother because it happened to her.
People are always more willing to deliver an objective assessment in the abstract, when it actually happens to your lovely old grandmother who spent years in Nigeria in her youth helping their education system the cause-and-effect of judgement suspension is easier to follow and natural sympathy for a member of your tribe comes into play.
The tragedy is that people with a strong belief that you are correct result in a less resilient population. Believers who end up in politics attempt to create a legal environment based on the idea that people cannot be trusted to think, a self-perpetuating cycle once it gets bad enough - if you don't normally have to think while going about your day to day activities, it becomes harder and harder to blame you for not thinking when anything unusual happens, so more and more things have to be regulated to the point where it is impossible to come to harm no matter how stupid the action.
Not only is such an environment unsustainable (at least given our current technology level), it is severely counter-productive. Safety is easiest to apply to a narrow range of possibilities, and thus laws are made which subsequently restrict peoples ability to act in an intelligent, but uncommon manner, resulting in heavy efficiency losses overall.
So jidar, why are you mis-representing the views of people in order to make yourself feel superior, and why are you screwing up my society?