I don't think anyone is actually arguing that carrying luggage during an emergency evacuation is anything but wrong. However I think the psychology bears some examination.
There's almost certainly a distinction in many passengers' minds which may arise in these situations. If the threat is plainly visible and imminent - say a fire inside the cabin - I doubt if many people would prioritise their spare undies over an immediate swift exit, unencumbered. However if the evacuation is being initiated in response to factors known only to the flight crew and not obvious, I suspect many passengers would think "may as well..." It's a fact of human psychology that we are inclined to think that bad outcomes - like death - always happen to someone else.
Personally I've always carried the absolute essentials on my person rather than in cabin baggage and can't imagine why anyone would do otherwise. As for the issue of excessive cabin baggage it infuriates me as much as it does professionals in the industry. However having had hold baggage lost five times (on one occasion permanently) it's hard to resist the temptation to carry on sufficient semi-essentials to cover the possibility.
Given the gravity of a situation requiring emergency evacuation, I'm surprised that it's not accompanied by PA instructions (language limitations accepted) forcefully ordering appropriate procedures - like NO baggage. It'd have to help, I'd have thought.