While I do yoga at home now, I took classes for 3-4 years at my old health club and then did a summer class at a studio for 10 weeks (yoga and meditation).
The instructors at the club were all certified (mostly Kripalu) and only one wanted to actually make a physical correction (she asked). The others would stand by you and verbally talk you through corrections, although I think they did touch some people. But, nothing that I would consider to be manipulation.
When I was a group fitness instructor, I was taught to always ask if I could physically correct someone, although I rarely had to, because usually I could talk them through changing their incorrect body position. Some people never changed their bad habits and I didn't harass them. For some reason, some people either don't want to hear you, or they really can't do what you are asking.
When I started yoga, I didn't like the spiritual aspect at all. When I relaxed a little, I enjoyed it, even though I am not a particularly spiritual person. When instructors start getting "too" spiritual, though by talking up their specific view points, almost to the point of therapy, I don't like it. Yogais a system of psychotherapy, dating back thousands of years. What we practice in the US is only the tip of the iceberg. The average instructor is not qualified to use yoga this way.
I am currently doing research on the neuro-chemical effects yoga has on anxiety. There's some cutting edge stuff being done at BU, showing that yoga increases the production of chemical neurotransmitters (GABA) that decreases anxiety, in much the same way physical exercise does. This stuff is real, but, again it's not what you do at a studio or gym. This is one reason why I am considering yoga certification, to eventually build a practice that combines psychotherapy and yoga (controversial, but quite common around here).