A friend of mine owns an airplane, and his brother is a pilot in the USAF. I asked him this once and his opinion was that 2 engines makes the plane more complicated and increases the chance of pilot error. He had suffered 2 or 3 engine out incidents in his single engine plane, and landed all 3 with no issue. Obviously if your plane doesn't glide very well then the redundancy of a second engine is necessary (i.e a jet), but in your typical Cessna-esqe plane, gliding is a viable option.