I actually think it also comes from a lack of understanding. Many people don't know what DnD actually is, they just take that information on spoofs and comedies of the game they see on TV or the internet. Or some are just really conservative with religious backgrounds such as my mother. The first time I told her that I played Pathfinder, she said, "What?! That is some demonic stuff Josh, people have died playing that game"! Of course she was referring to those few incidents in the 90's were some guys from Europe took the game a bit to far, but I basically just had to explain to her that there was nothing wrong with, it was just a game of pretend with rules, and dice. Luckily I was 20 at the time and there was not a damn thing she could do about it, it's not like I was holding the events at her house.
Kinda goes hand in hand with why DnD is considered the ultimate geek thing because it is the weirdest thing to comprehend and understand by people who don't actually know what goes on in those games. They automatically assume that we dress up as wizards and thoroughly believe for a brief time that we are, that we get so far beyond reality it's automatically unhealthy and quite frankly, weird...as if DnD players were taking some kind of weird drug, or as if we had some kind of cult mentality. Lack of understanding friends, that is what it comes down to.
It also doesn't help that DnD is usually a private event. I don't know about you guys, but when I DM a game, I do not want anybody around except for the players because I feel self conscious when trying to throw my accent for NPC's in order to tell a more engaging story. I would guess to onlookers who are pretty much barred from entering the area, the whole DnD thing might seem a bit strange. It is unknown to them, and people are cautious and fearful of the unknown.
I think those are some of the reasons why DnD is considered kinda of the ultimate Geek low by some groups of people.
