Many game designers prefer to have the character you're playing be silent. This technique has also been shown to be effective in creating Role Induction.
Grand Theft Auto III is just one of many, many examples. By not giving the character a diamond or even any speech at all, each player can take the badass role and make it his or her own. Still, most players I've spoken to preferred playing Tommy Vercetti, the character in Vice City who does have a voice.