In many ways Travis Bickle, the disturbed taxi driver in Scorsese’s famous film, is a model of public engagement. For one thing, he really thinks about his audience. He rehearses in front of a mirror so that he will be fully prepared for his encounters with the people he wants to reach. Legs apart, arms folded, his stance is confident — his body language is really very good. Then, with the merest tilt of the head: “You talkin’ to me?