From the beginning the FAA has treated jets differently. In almost every area of certification the standards for jets have been more stringent than for propeller-driven airplanes, and one of those jet standards had been a requirement for two pilots. That rule remained in force until 1977 when Cessna won approval for single-pilot operation of its new Citation I-SP, and now many models of business jets are approved for single-pilot operation.
Most business jets are certified in the transport category because they have maximum certified takeoff weights greater than 12,500 pounds, the demarcation between large and small aircraft. One of the many certification rule changes between small and large aircraft is a requirement for at least two pilots in the large transport category airplane.
It's easy to understand why two pilots would be required in a transport airplane, given the greater complexity and generally higher performance. By their very nature transport airplanes are designed to carry larger numbers of people, or a greater amount of cargo, so there is a greater risk to a larger group, and certification theory has always demanded a higher standard as risk increases. Society, through the FAA, grants us wide latitude to take chances with our own lives, or with those of a few friends or family members, but that all changes when passenger capacity increases. Nobody wants to operate really large airplanes - including larger business jets - with a single pilot, but light business jets are a different issue. For many people a single pilot in a light business jet is enough.
It is understandable why some owners would want to fly their business jets without a copilot. The convenience of taking off when you want, staying as long as you want, and all other aspects of operating your own airplane are at least a little more complicated when you need two pilots. Single-pilot operation is all about flexibility and convenience. There is some cost to be saved by not hiring a copilot, but that's not a big issue. Besides, you almost certainly will pay more in insurance premiums than a qualified copilot would cost to hire.
Many business jet owners will argue that single-pilot flying is safe, but no sane person would say it is 100 percent as safe as with a well-trained crew of two professional pilots. But in all forms of general aviation flying we trade a small amount of safety potential-a second pilot, or maybe second engine-for convenience and availability. If we didn't make some small compromises on potential safety, we would all be on the airlines because they adhere to the most rigid, and potentially safest, standards.