I would say as a generalization- yes it is. I mean it disables us from clear and fluent communication and impedes us from speaking altogether at times. Whether it is a psychological or physical disability, I think there is room for debate because it could be physical where some component that allows us to create speech is impeded or psychological in that something within our brains is functioning incorrectly. But i'm no expert and the more I think about it, the more dumb I feel.