I agree with the essence. Judging by your testimonials, you're probably a mild stutterer (like myself). In this case, it is in fact true that our stuttering, or the way we speak in general, is largely influenced by our environment/social context and how comfortable we are in it. However, I don't think our friends who are on the more severe side of the spectrum can just be more confident and stop stuttering. However, I'm sure that it nonetheless plays a role. I see the "solution" as part speech drills and part work on oneself. If you only do one, you'll only go this far.