A strong statement I think can be said in Serling’s defense is that even if he did serve “as a pitchman for products from beer to socks to floor wax” that work has been almost entirely forgotten by everyone except Serling biographers. Not that there’s anything wrong with biographies, but the reason Serling’s life is of interest and worthy of study is because of The Twilight Zone, not because of his work as a pitchman.
He was a complex individual who did things that, at the time, might have seemed to be undermining his goal of improving humanity, but the legacy of The Twilight Zone has outlived the advertising he did. And maybe he hoped that would be the case.
This is probably addressed by Horowitz (I admit I need to RTFA and will), but since the snippet here focused so much on Serling selling “beer to socks to floor wax” I felt compelled to say it.