So you have to go back fifty-five years to find one positive effect for back channels?  Great!  Let's not concern ourselves with back channel  comms!  We should just ignore that we could go back another fifty years and find plenty of examples of bad results (WWI).  Hell let's ignore that we can go back less than that and find some examples of Executives using back channels in detrimental ways.  Pay no attention to the man behind the curtain of the Iran-Contra affair.  Even accidental bad results like under the Obama administration's Operation Fast and Furious.  No, no, no, no, no!  There's no worries about Trump and his administration and their months of changing stories, revising history, and outright lies- oops, I mean "alternative facts," when it comes to back channel comm-OW!  OW!  Oh my.  I think I pulled my hyperbole muscle.