The soldiers of UNIT are hardly the bane of the Doctor’s life, but they do excel at complicating matters. Then again, in his experience that’s a trait shared by most military organisations. They come up with all these rules and regulations that must be obeyed, then go around brandishing weapons and killing anyone who doesn’t agree with them. They’re like a bunch of naughty children, only a lot more dangerous.
He’s tried to teach them, his Third incarnation even worked with them for several years, but they never learn. One of these days they’ll probably be the death of him.