The fundamental problem with the space shuttle program was the same basic problem that NASA had post-Apollo 11; there simply was no appetite on the part of either the public nor the political leadership for any potential follow-on missions that would justify the kind of funding required for successful completion of those programs.
As the document referenced in post #57 made clear, the design of the shuttle system - a re-usable vehicle with a pretty small payload, launched with the aid of two massive solid-rocket boosters and a disposable tank - was chosen because it was the cheapest to develop at a time when NASA budgets were being pared back significantly in real terms. They knew at the time it wouldn't be the cheapest to operate, but they weren't given the money to develop a better or more sustainable program.
To give one example of the choices forced on NASA after Apollo 11, the last three moon missions were cancelled, even though the hardware was built, and even though the cost of launching those missions was a tiny fraction of what had been spent on the space program, which had been driven entirely by the goal of getting to the moon. Yet NASA cancelled almost 1/3 of the moon missions - although hundreds of billions in current dollars had been spent to develop the capability to launch those missions - simply to free up some cash for shuttle development, because they weren't allocated the money to do both.
The ultimate irony of the shuttle program was that it was most designed to build, service and re-supply a space station - which was, due to budgetary constraints, abandoned pretty early on in shuttle development. It became a machine with the sole mission of flying people into space to do - what?
No doubt NASA made some bad decisions post-Apollo. But the fundamental decision that crippled the space program was the decision by the political leadership and the American people not to have an Apollo-scale space program at all.