Stop doubting yourself and start believing yourself. Who cares about what people think about you. Just because you stammer, it doesn't mean that you are less smarter, caring or attractive as a person. There are assholes and actual people in this world. Don't pay them any mind, they are the real losers. Be glad that you at least have a voice. There are some people that don't have arms, legs, fully functional brains and even voices of their own, if anything, you're the closest thing to being normal (no disrespect to those who are affected by the previously mentioned).