I always believed that driving on the left-hand side was safer because, a majority of the world's population is right handed. So, you want your good hand on the wheel, when you are changing the radio or using your stick-shift.

Other than for legacy reasons, right hand driving is harder than left hand. The easiest way to illustrate this is to learn to drive the stick-shift: it is easier on a left hand drive car (with your left hand on the stick-shift) rather than a right hand drive car