On most forums, I'd agree with you 100%. This one, though, is for folks with mental disorders, and as often as not the members would rather things not stay there indefinitely to decrease the chances that people they know find out about some of this stuff, because with the way things are today, just about anything outside the utterly normal could threaten your job.
Not to mention, there's a subforum dedicated to silly games like word associations and "musical artists a-z" sort of things, and there's absolutely no need to keep any of that long term (or even mid-term...).