It's not that the drivers are inherently evil; it's their situation, and I don't envy it at all. The only way for a hack to make money is to literally race from fare to fare. A cab driver makes the bulk of his wages on each new pickup, the shorter the ride, the better. Also, they're all competing for the same fares, so a turn signal probably is a competitive weakness. It's like Zidane pointing to the lower left before he takes the penalty kick....
Plus they're driving cars that they don't own!