I've recently seen the following (actually very long and well accepted) question on MathOverflow. Examples of common false beliefs in mathematics. Which I think is a great "question" and one can learn a lot from such a post, because the thing about "common false beliefs" is that they are common.
I searched Physics.SE for such a post and of course didn't find one. Then I thought "okay maybe I could start such a post", recognizing that the "big-list" tag description explicitly says not to ask such questions.
So why do we ban questions like the one on MathOverflow cited above?