I agree. The immediate aftermath of a high altitude decompression will mean lots of alarms going off, extreme cold, frozen over windows, massive windstorm if it was a cockpit window that shattered, etc. No one is going to be thinking clearly for the first few seconds, and as short panic would be a perfectly normal reaction. Best to have it on, just in case, since it's only you up there.
Plus . . . you never know who's looking up from the back when the door opens to let the other guy in . . . .
Apparently, they have not seen the decompression video that used to be shown in most recurrent ground training sessions. It is quite sobering to watch, especially when you see that test pilot's eyes roll up in the back of his head!
I guess some people don't understand why there are rules, regs, and policies. Over time, they have usually been created because of an accident, incident, loss of human life, and some idiot saying, "hey, watch this!"
Maybe, that's why they put pins in handgrenades, a safety on a gun, seat belts in cars, and require pilots to don an oxygen mask
when another crewmember leaves the cockpit above 250. It's about the passengers in the back, people on the ground, and the investors that gave you that $25 million airplane to fly! It's not about you! They pay you to fly the airplane by the rules, anything less is gross negligence. Be a Professional, follow the rules!
You can puff your hair up later before you stroll through the concourse showing everyone you are a pilot!