As a counterpoint, and in the interest of fairness, I knew people when I was in college who were seriously into their gaming fantasies, to the point of being scary. People who seemed to have a hard time separating their gaming reality from actual reality. They scared me, kept me from getting into the game scene for a couple of years.
I finally realized that these few people were the fringe, the ones off balance enough to stand out. They were unwilling or unable to accept how mundane their life was, and were bound and determined to invent a new one. If it hadn't been games it would have been UFOs or James Bond, or maybe they would have become conspiracy nuts, like the ones who claimed that D&D books were enchanted so they couldn't be burned, or that the miniatures couldn't melt or be broken. (Yes, I've heard from that camp as well.)
But D&D didn't mae these people crazy. D&D was just the focus of their crazy, at least for the moment.