I also came to the same conclusions when self analysing my stutter. A genetic predisposition which was initialized by my environment, which then got worse in high school, daily morning register, presentations, loud readings, group discussion, then the anxiety and fear took over. I then developed tricks and coping mechanisms, which probably led to the classical conditioning mentioned in the theories. The next phase of my analysis happend when I volunteered for a university research on Tanscanerial Direct Current Stimulation effect on stammering at Oxford university. Previous research comparing speech fluency , coordination, articulation, anticipation parts of the brain between fluent speakers and stutterers revealed that we had less brain activity/"connections" in the speaking part of our brain. My brain scans confirmed this, so now I don't know whether the brain confirmation is due to genetics or years of being quiet & disfluency.