I have always, and will always, continue to agrue that the entire point of having manned space flight is to actually go somewhere. There is simply no reason to place humans in space unless we are going to another world. Zero.
The space shuttle and its bastard child, the Space Station, were completely dependent on the existence of the other. While NASA had grand plans for post-Apollo Mars missions, congress was never going to give them the funds necessary. We beat the Russians, mission accomplished, time to move on. So they settled for what they could get, the Space Shuttle. Unfortunately, instead of having a clear idea of the shuttle's purpose and applications, they tried to market it as all things to all parties and ended up with the flawed machine it was...