Set and setting are key for any psychedelics. It's unfortunate you had a bad trip. Psychoactives such as MDMA and Mushrooms are beginning to be used to treat all sorts of mental disorders. Check out MAPS.org. So It's all about doing it in a comfortable place where your mind is at ease I think. As for stuttering, I think it can trigger realisations that might help one to decrease bad stuttering habits and therefore increase fluency. It's not a magic pill but can bring about realisations to help change ones life that could have taken a lifetime to figure out. I don't condone the use but I don't think they should be disregarded either.