same thing as with certain types of substances. you may have a really good or a really bad experience. at least with meditation there is some work (a lot actually) involved and along the way you get a chance to process some of the things that happen to you.
I witnessed one of my friend's psychotic episodes and it was probably the most terrifying thing I've ever seen in my life. They went from being the completely normal and wonderful friend that I'd known for years to (over the period of about 8 hours) slowly feeling like they could see and understand more and more about the universe. Finally they felt that they were a god and had a duty to overthrow a consipiracy against the world that only they could see. I luckily managed to persuade them to go to a hospital and after restraints and drugs they were perfectly normal again the next day.
Even as I say that the meditiation experience may have "triggered" the episode in the author, I don't understand enough about the condition to even say that this is probable or even likely. One of the things I learned about my friend's condition is that this feeling of knowing more than others, or "seeing the world as it really is" tends to bubble up leading to the very rationalisations that are used to deny the illness. My friend is very, very bright (and this seems likely to be the case for the author as well). Creating a running dialog of plausible explanations is easy for them.
I guess what I'm saying is that meditation may or may not have a dark side, but I'm relatively sure that the author's experience is not related directly to the meditation. It was an existing medical condition.
People damage themselves in all kinds of ways when they are unsuited/poorly trained/ prepared for extreme environments.
You wouldn't expect a grossly overweight person to run 11hrs a day for 10 days. Goenka's practices are extreme, and the 10 day silent retreat isn't suitable for everyone.
This is why there's the questionnaire for Vipassana during enrollment: it's an attempt to recognise someone who's not fit enough (yet) for it. That the author was able to persuade the volunteers, despite his known past, to let him in should not really reflect against them.