I'm curious if showing a date is as bad as he thinks
I predict yes, but if I'm reading his position right showing the date is just a symptom of not having a Long Content focus, which is what he's really arguing for in that article (and which your site already has in spades).
If the problem is focusing on short-term writing which becomes worthless quickly, then simply hiding or showing dates shouldn't much affect how long readers stay on the page: most short-term stuff shows its colors very quickly. (How many sentences does it take to figure out you're not interested in a rant about John Kerry from 2004?)
Another month has passed and here is a new rationality quotes thread. The usual rules are: