The Doctor and soldiers. A quote from interview with Steven Moffat from DWM #477

Making Danny a former soldier both mirrors and sits uncomfortably with the Doctor's morality.
"The ultimate hypocrisy at the heart of the Doctor, which is fun to poke a stick at, is that he's so nasty about soldiers and about people who carry guns, yet look at him - always in the middle of the fight, usually taking command, and I'm not so impressed at his refusal to pick up a gun when he's inclined, occasionally, to blow up entire planets! I think Danny Pink would say, 'Look, I picked up a gun to save that guy's life. You blow up a planet, and you sod off.' And I think that's a good character trait of the Doctor's. I like that he's the ultimate autocratic liberal - you know, the fascist liberal. It's what I love about the Robin Hood thing, because it reminds us that the Doctor never stops being a nobleman. He's a high-born nobleman, used to wealth and privilege, who decided to come down among us lot and help out. He thinks he's one of the guys, but never stops assuming that he's in charge and that people will make him tea. You love the Doctor, but you do think, 'You're a bit of an arse, and you really, really do think that everybody's here to carry stuff for you.' That's true throughout the Doctors, however 'men of the people' they pretend to be. They're really wonderful men trying to help everybody, but the Doctor does, just like Robin Hood, expect to be in charge. He doesn't really tolerate being second in command. He's helping out the people, so long as he can be the boss person with the best bow and arrow - and one day that will come back to haunt him."