I think it's about feedback. Most stutterers don't stutter when they are alone and talk loudly to themselves. In that case, there are two voices and two listeners, the voice in your head and the outside voice. You hear your inner voice and you also hear your own outside voice. When someone comes that can hear you speak, that person becomes a 3rd listener. I believe human beings automatically put themselves in the 3rd listeners shoes to manage their tone/ volume when they wanna talk to that person. But with stutterers some glitch happens here. So the feedback that the brain requires to know that it is speaking correctly, will not be provided and the brain tries to find another way to spit the word out, and that causes the stutter. So a stutter in my opinion is the brain's way to actually say something. Not stop you from saying it. The real stutter happens before you say anything.