Okay, so first off as a person who's had experience with an actual Himalayan Yogi, most of what Black says is true.
These Yoga classes are usually a contracted form of what the Yogic monks practice and therefore if carried on unchecked can be quite dangerous.
Yoga (for a first timer) starts of primarily with simple postures and more importantly breathing, and there are absolutely NO difficult postures for at least the first six months. Then he/she learns two new postures over a period of two months and adds that to their usual routine, and this iterates.
So, in about two years the person should be in good physical shape. That is how Yoga should be done.
I'd recommend an immensely useful book on Hatha Yoga, but I can't find the link. I shall add it as soon as I do.
Yoga is a quite like going to the gym, except you don't need a gym and it affects your whole body within the same time, not just whatever body parts you work out.
I spent about half of last year living at a Buddhist monastery and one of the other people staying for part of that time was a yoga instructor who talked about the same things. I've meditated for some years now and one of the main things he had me pay attention to were the smooth transitions between poses and quality of breath in particular. He seemed to agree with an observation I made about it being much like breath meditation with movement added in. Keeping a steady and concentrated mind with careful movements that flow together with the breath were important to maintain and he only gave me a handful of simple poses to work with, things like just raising and lowering legs and turning my legs to the side. No fancy poses or anything. He talked about the ignorance of many yoga instructors too and how dangerous it can be if not taken slowly and with great care.
I'm no yoga expert, but I've dabbled at two separate points in my life. While I've forgotten practically all of the postures, the breathing stays with me. I still consciously use different types of breathing depending on whether I need to increase/decrease alertness, relax the body, etc. IMO everybody should learn these important life skills even if they have no interest in anything else yoga-related.
He writes "my experience is that most yoga teachers encourage moderation". I've lived in an ashram in India and gone to a number of classes here and there and my experience is that the majority of yoga teachers are dangerously incompetent. Sure they talk about moderation, going slow, listening to the body etc but generally they still get people doing poses that are probably dangerous for a person in excellent shape and they almost universally fail to train people in the fundamentals. Partly its the fault of impatient students who don't want to spend a whole series of classes just learning to sit and stand properly (even if it's what they actually need). I still do a little bit of simple yoga now and then - it truly is excellent for fixing occasional back problems but I don't think I'll ever take another class, at least not without knowing the instructor very well.
The rebutting-author makes a valid point, but he seems to entirely miss the point. Yes, the yoga piece is no different than a "How Running Can Wreck Your Knees" piece, but yoga is especially treasured because it's seen as a spiritual, theres-no-way-something-this-inner-peaceful-could-be-bad activity.
The danger is not just in the physical exertion, but the mindset of the practitioners and teachers.
The danger of overexertion, which as you said is obvious, is not the only take-away I got from the article. Many of the worst injuries described came from poses that are not necessarily strenuous/difficult, but that rotate or bend the neck out of standard range.
