There is no such things as a yoga class with “no spiritual component whatsoever”. Spiritual content is in the DNA of yoga.
This is not merely a Roman Catholic perspective:
http://www.lighthousetrailsresearch.com/yoga.htm
Yoga is dangerous to anyone’s spiritual (i.e.: actual) well being.
Perhaps where we could find common ground here is that there are classes that are called "yoga" that aren't -- they are purely physical exercise. I've attended some of them.
Religions, by the way, don't have DNA. . . . they are taught. And whether yoga is harmful or not depends entirely on what is taught.
Thank you for posting that link. Oftentimes what begins as an innocuous exercise can, over the course of time, draw the unsuspecting individual into something much deeper.
You are quite right in that there IS no such thing as a yoga class with no spiritual component whatsoever IF you take it from one of the standard yoga houses, that is, Shivananda, Iyengar, Bikram, Sachidananda (Integral Yoga), etc.
Today, there seem to me more NONspiritual yogas than not. Fitness studios, gyms, fancy-schmany clubs, schools (colleges, universities) and one-man shows usually do offer the generic yoga. They probably wouldn't last in the yoga business if they did anything else.
My 2 cents.