Stuttering doesn't stem from a psychological problem. You're drawing a erroneous conclusion. We don't stutter because we are nervous or scared or any other emotion. We are nervous/scared/etc. because we are don't want to embarrass ourselves, feel out of control, having people judge us, etc because of our stutter. And those fears in themselves double back and hamper our speech even more. it's a shitty cycle, but it doesn't show that stuttering stems from a mostly psychological problem. Have you ever stuttered when you weren't nervous or around people you were comfortable around? I know I have. http://www.westutter.org/who-we-help/causes-of-stuttering/