If you are going to write a letter like this don't put this: "Scientific American published a bewilderingly flimsy opinion piece" in sentence 2. Instead write "we strongly disagree with some of the conclusions of your piece".
The whole letter reads like a polemic attack on the editorial department of Scientific American.
It would have been quite possible to have taken the arguments in this piece and written a firm rebuttal that gave an alternative view and set our the weaknesses in the published op-ed - and I suspect it would have been published in its entirety.