Yoga has been around for thousands of years repeat a matra or totally imerse yourself in some object get the brain firing in a certain state or rythm and a new way of seeing the world now changes you and if you let enough unconscious become conscious you end all suffering for your self as you are no longer ego centered and now live life in a different way that sees through the illusions. Ending all desire ends suffering which is a pretty neat trick if you can pull it off.
So I wouldn't classify it as evil but helpful for those seeking enlightenment as it makes one more prone toward getting those mystical experiences that gradually enlighten one to become a Buddha. I'm not to keen on all the hard work and the iffy out comes I'd rather work with magic mushrooms, and other like substances I think it is more quicker, and if done right can lead one to the same place as the Buddha at least that what John Hopkins is saying with their research on some of these chemicals.