Why do people think yoga is evil and makes you not a christian..that is just to ask?

I was reading about Bono and Sting's religous beliefs and someone made a comment that sting did yoga so he couldn't be a christian...Bono is a very devout christian...due to their christianity and the conflict of rock n roll....U2 almost never was!! They prayed and felt secure enough in their convictions to carry on.