Some say this is an "inevitable" result of pushing boundaries. No. This is the result of a poorly managed program. What they are doing is much easier than the Apollo program, which was well managed and had no in-flight failures that resulted in loss of life, while accomplishing an infinitely harder task.

This is a tragedy, obviously. But the program is about six years behind schedule, been going for 10 years. The most stupid thing they've done is stay with an experimental rubber/nitrous hybrid engine this whole time, instead of switching to liquid/liquid engine, a well proven technology. I know first hand that groups with such engine expertise have approached Virgin and been turned down.

Seeing only the first paragraph, I already know that some rubber in the hybrid engine detached blocking the nozzle and causing the whole engine to explode. The pilots should have refused to fly until Virgin had 10 consecutive motor qualification tests at full duration, not ride on a ship with a half-baked motor that has seen constant modifications during the last year.

In the software development world, a "death march" in a program behind schedule does not result in loss of actual life, not so in manned spaceflight.