This kind of thinking a common fallacy.
For several reasons.
An observed trend in one piece of population, doesn't necessarily have it's causes within something intrinsically related to INTPs or the INTP psyche.
These forums tend to attract people who are in some way troubled; maybe they are lonely, depressed, or just looking to find a place of kinship after prolonged periods of real or perceived isolation from their peers or humanity at a higher level.
Specifically talking about depression, it causes us to get more withdrawn and introverted, more contemplative and analytical in the purpose of problem resolution, hence you will find that many people tend mistype themselves as a consequence of this, which leads me to my second point.
You would be mistaken to acknowledge most trends you spot on these forums as manifestations of a particular type, as a lot of people tend to not belong to the type they claim.
Lastly, we pretty much have a shortage of information to make qualified conclusions about this, and most people will use anecdotal information, which is a lot less than ideal, and can be outright misleading, taking into consideration possible mistypes and differences between individuals.
My assumption is that things like individual brain physiology, chemistry and external stimuli you are subjected to are more relevant where these kinds of disorders are discussed.
Which isn't to say that a correlation stemming from your cognitive function doesn't exist; this apparatus does influence how you perceive external stimuli and react to it, its shortcoming is that it's simply less reliable than looking elsewhere at this point, and it doesn't quite get to the root of the matters yet, because it's really more of a descriptive method.
All of this assuming you're after pinpointing the exact causes of your ailments.
I don't think any type is inherently predisposed to any kind of pathology. Cognitive functions are neutral in an isolated context. The pathology happens as a product of various elements, and if you're using cognitive functions to figure this out, you're going to have settle with speculation.