Based on what i know, and as an engineer, I offer the following:
Somebody made a decision based on insufficient engineering. Whether it was an engineer or a manager, I don't know. It was made, with disastrous results. This resulted in failure of the cement plug, and the exit of a whole lot of the drill string from the hole.
Everybody focuses on the BOP. The BOP is a last-ditch line of defense. This focus, to me, is like focusing on the fact the parachute didn't work when the pilot had to bail out of an airplane when the wing came off.
Whether the BOP was damaged by the blow-out, or failed to work because it was improperly installed/had a dead battery (why rely on a battery?), or was simply a boat-anchor, I don't know. The disaster resulted from the things that occurred prior to the BOP failure.
Engineers make mistakes, being human. that mistake may have come from insufficient information, bad data, incompetence, inexperience, economic pressure, or being overruled by management, among other things.
Now, there are lots of Federal regulations and guidelines for all sorts of things. But, you cannot have regulations and remedies for all things ("I want a list of all possible unforeseen difficulties on my desk by 4:00"). We go with "best known engineering practices and procedures" when in doubt.
We have licensing requirements, dictated by governments, (and designed by engineers) for engineers, just as we have for lawyers and doctors of medicine, to ensure a minimum competence. Companies have internal procedures-reviews, conferences, etc.) to supposedly put the right people in the right place, and ensure competence, supposedly. (Unfortunately, in many instances, competence is defined as "who can play the internal political game best", just as in our political leaders.)
Whatever the reason, it happened. Nobody-not BP, not Obama, not Bush, not the Military- can prevent that. I don't know if a different BOP could have stopped it once it started, and neither does anyone else here.
I have no doubt that the best minds and engineers available are working to stop things from getting worse. Let's let them work. In the meantime, we have to do the best we can with what we have to clean up. We have good minds on that, too. Let them work, and keep the politics out of it. Give 'wm what they need, and get on with it.