What is this myth? Double clutching saves your synchros and takes the load off of them. Try it with any manual and you can feel much less effort shifting.
"While double clutching is not necessary in a vehicle that has a synchronized manual transmission, the technique can be advantageous for smoothly upshifting in order to accelerate and, when done correctly, it prevents wear on the synchronizers which normally equalize transmission input and output speeds to allow downshifting."