What if people honestly believed that they were actually going to make money if they shuffled things around in the way that they did? What if they thought that

What if people honestly believed that they were actually going to make money if they shuffled things around in the way that they did? What if they thought that the risks from the bad loans were acceptable because of bad simplifications in their models? What if this is explainable by stupidity and not malice? People are stupid, but they're not (usually) deliberately self-destructive.