Does Everybody Know What Everybody Knows?

I have another one of those phrases that should make you leery: Everybody knows.
Isn't it amazing how, almost every time this phrase is used, it is used to cover some controversial subject that is only being discussed precisely because everybody does not know, or at least does not agree? Yet someone, at some point in the discussion, will throw out the phrase, "Everybody knows (insert your favorite controversy here)," and this person will act as though he or she has uttered some profound truth, which no one can possibly argue against.
That is, of course, the entire purpose of the phrase Everybody knows. It is almost never used to convey information that everybody does, in fact, know. If everybody knew a thing, in a controversial discussion, there would be little point in saying it. You would be that loser who only points out the obvious. These people, however, pontificate with the air of a prophet, not of a loser. They are not pointing out something that everybody knows, nor are they trying to point out something that everybody knows. They are pointing out something that they believe and want everyone else to believe, but they do not want to have to go through the effort of convincing everyone else to believe. If you disagree with them then they want you to believe that, in this context, "everybody" means "everybody other than you." They want you to believe that you are the only fool who does not know this thing and so you are obviously ignorant and not worth discussing. Case closed.
In most situations, the case should be closed, but not in the manner the user of this phrase believes. If a person has to resort to such a fraudulent tactic then obviously that person is probably not worth discussing. If this particular derailment does not work, that person will most likely move on to yet another derailment attempt and nothing of any consequence will ever be achieved.
If someone is trying convince you that your position is foolish but cannot be bothered to offer any reasons why, dismissing the subject with the high and mighty Everybody knows, odds are good that person has just proven their own case foolish, or at least lacking in evidence. The fact of the matter is, when it comes to controversy, there is almost nothing that everybody knows. Otherwise, it would not be a controversy.