Many years ago, early in my career, there was an argument that existed, that if a deaf child was taught sign language, it would be a disincentive to speak. One only has to spend some time with deaf adults to see that they communicate using all of the tools available to them, including sign language and speech, and while speech might be how we are programmed biologically, even greater than speaking, is our desire to communicate, in all the ways necessary including: voice, gestures, writing, facial expression, and so on.