Voodoo doesn't violate someone's freewill. Keep in mind you have the freewill to give up your ability to have freewill. Believing that external things can hurt you against your will is giving up your freewill.
I was going to say the exact same thing. Can't help someone who refuses to be helped naskat. I'd say give love show love and give your influence to bring them to a positive spectrum, but otherwise not much you can do.