Evil can infect anything, including mainstream religion and Christian sects. Unlikely, Yoga as exercise alone, can have that effect. Most people are not religious anyway. When you become a maniac about anything, be it yoga, sex you risk losing your mind. However Yoga, taken in entirety, attitudes, diet etc, , is a way of life, and cannot be separated in total from Hindu philiosophy. It can become an alternative to religous faith.