Check out Stanford's Encylopedia of Philosophy entry on double-effect: http://plato.stanford.edu/entries/double-effect/ . Essentially, double-effect means that your good actions can have unintended yet foreseen evil consequences. If you make a hunting rifle, and someone uses that to shoot children at a school, are you responsible? Not an easy question to answer.
Someone driving a car into a crowd does not make it Ford's fault. Society does not ban cars just because 50,000 people a year are killed by them.