There were times the Doctor despaired. Humanity had potential, but they were so scared of everything, including each other, that they armed themselves to the teeth and did battle with anyone they didn’t understand. If they couldn’t even get along with their own species, what chance did people from other worlds have?
Admittedly, many of the otherworldly visitors who came to earth did so to destroy, invade, or enslave the planet, but did that give UNIT the right to greet every alien species with an array of military ordnance and a show of deadly force?
The Doctor didn’t think so.