If stutter was a side affect of stress and anxiety two things would happen. 1 stutter would be completely eliminated by anti anxiety medication such as xanax. 2 all people in stress inducing situations such as war or financial instability would stutter, and yet we have completely relaxed people who stutter and highly stressed people who talk fluently. Yes, anxiety amplifies stuttering but it's not the cause of it. Speech for 99% or more of population isn't affect by stress just like walking, breathing or blinking isn't affected for stuttering folks. For 99% of the people speech is just one of the thousand things that body does. Stuttering might be neurological problem and human brain is probably the most complicated thing in universe, the cause and the cure might be beyond our current level of science. I hope I'm wrong tho