Air bubba
First Officers taxying the aircraft? Next they'll be wanting landings too. Outrageous
Actually in my experience, in the UK, FOs taxying is SOP when it's their sector. Perhaps in your company and/or location it's different. It's all part of this wacky idea of developing the next generation of aviators. Role reversal I've heard it called.
As for the memo that started this thread I cannot fault it. I know nothing of the politics at United but I read it as an impassioned plea to the flight crew to do their jobs professionally. A former trainer said to me that "Fate is the hunter" should be required reading on a conversion course and I believe he was making a valid point about never letting your guard down. Be safe out there 'cos someone or something is going to try and spoil your day.