Well, when you say "not responsive to civilian control" you're kind of glossing over a lot. MacArthur had given Harry Truman a string of deliberate insults, and repeatedly brushed up against insubordination. At the Wake Island conference he failed to salute the President, and generally treated him as contemptible. Things never really improved from there.

The biggest issue with MacArthur's behavior was that he couldn't accept that the President set policy, not MacArthur. This is where he really showed that he was 'not responsive to civilian control." MacArthur was told by the Executive branch that Chinese territory was not to be attacked, but rather than accepting that and moving on, MacArthur repeatedly asked for it to be changed, incited congressmen to cajole the President about it, and even sabotaged potential peace talks by broadcasting a demand for Chinese surrender without consulting the State Dept first.

And there was also the war situation on the ground. At the Wake Island conference, MacArthur had repeatedly assured the President that China would not enter the Korean war. MacArthur then defied instructions to use only S. Korean troops near the Chinese border, but rather used UN (mostly american) soldiers and marines. This of course provoked China into handing the US it's worst battlefield defeat since First Mananas.

If you want more detail about the MacArthur/Truman conflict, I'd suggest "The General vs. the President: MacArthur and Truman at the Brink of Nuclear War" by H.W. Brands. If you want more info on the military history of the Korean War, a good recent book is "The Coldest Winter" by david halberstam.