He’s a petulant child who cares little to none for others than those who give him money or hang on his every word and is doing his damnest to destroy the environment.
It would also explain his fear of stairs, after all wearing a full body suit disguise means it’s hard to see your feet on the steps or to judge where the next step is.
21ST CENTURY edit
In March 2006 the Passameer-Day branch disguised themselves as various humans holding leadership positions and attempted to seize control of the British government in an effort to start a nuclear war. Their ultimate aim was to turn the Earth into a huge nuclear reactor pile and sell its remains off as starship fuel. This attempt was foiled by the Ninth Doctor when he ordered Mickey Smith to shoot down Downing Street with a missile. (TV: Aliens of London, World War Three)
So much would fit into place if it was.