The fact is, most every boy knows how to tie this knot. When I went through Army training, in the rope practice sections the instructor warned us.  "When getting your bowlines ready for inspection, I don't want to see any examples of 'The Hangman's Knot'. We are here to test all knots made, so maybe we'll test that one!" They were kidding, of course. I'm pretty sure. But the point is, they had obviously run into it before, thus the warning. 

 As it happened, I learned it in the fith grade; it was not part of the school curriculum, tho (g). Some bits of knowledge just have inherent interest. So, I vote against a ban; it is not liable to lead to a rash of hangings and Wiki would be shutting the stable door, anyway.