Some of his points seem valid, but many to me just seem rather nit-picky. On the first "myth" he does concede
1. Few people actually saw the Challenger tragedy unfold live on television.
2. The shuttle did not explode in the common definition of that word.
3. The flight, and the astronauts’ lives, did not end at that point, 73 seconds after launch.
4. The design of the booster, while possessing flaws subject to improvement, was neither especially dangerous if operated properly, nor the result of political interference.
5. Replacement of the original asbestos-bearing putty in the booster seals was unrelated to the failure.
6. There were pressures on the flight schedule, but none of any recognizable political origin.
7. Claims that the disaster was the unavoidable price to be paid for pioneering a new frontier were self-serving rationalizations on the part of those responsible for incompetent engineering management — the disaster should have been avoidable.
With Christa McAuliffe set to be the first teacher in space, NASA had arranged a satellite broadcast of the full mission into television sets in many schools, but the general public did not have access to this unless they were one of the then-few people with satellite dishes. What most people recall as a "live broadcast" was actually the taped replay broadcast soon after the event.And since I was a highschool student at the time, I was apparently one the "lucky" few who actually saw it live. I remember it was a very scarring moment. For years I could not watch a launching of the space shuttle without reliving that moment, expecting to see the "explosion" (that apparently was not an explosion in the traditional since of the word) again.
As to the third "myth", I was already aware that the astronauts did not likely die until impact, but to say that the "flight" didn't end after 73 seconds is a stretch in my opinion. It seems to me that once the craft is no longer under the control of the astronauts or mission control, you can hardly consider it a flight anymore. Maybe it continued to be a projectile for a few seconds and then a falling object, but in my opinion, it was no longer a flight.
I really have no knowledge of the other myths he addresses, but because I see the first three as nit-picky and, in one case questionable logic, I have to wonder about the other points as well.