"Everybody knows...." This is really outrageous rhetoric

[Martin68]

12. If you precede a statement with the phrase "everybody knows" then it is highly unlikely the statement

that follows it is true. If everybody knows something, then there is no need to state that fact up front. It's like admitting you are either lying or very unsure of your premise. And, as the OP points out, highly likely that the speaker is desperate to persuade others to believe something that just isn't true.