The latest hero of the time-travel adventure series Doctor Who, David Tennant, claims at one point that he "used to have so much mercy." Which started us wondering: When was that exactly? When he condemned his former best friend to a fiery death while the friend (the Master) begged to be saved? Or was it when he consigned the mad scientist Davros to 90 years in suspended animation, with Davros conscious for every horrifying second of it? Watch our compilation of the Doctor's greatest acts of "mercy" from the classic series, and decide for yourself. (Background music is the disco Doctor Who theme, by Mankind.)
Heh. Out-of-context, the Doctor looks like a murderous bastard, here. Of course, that's because we don't see what led the Doctor to do the stuff here.
Let's take The Hand of Fear up there. Alien artifact takes over Sarah Jane Smith and others, uses them as pawns and gets them killed, nearly forces a nuclear meltdown and tons of collateral damage from a bombing run. After said incidents, it manages to get a body. The Doctor offers to take Eldraad, said body, back to her (actually his) homeworld. There, Eldraad readily admits to GENOCIDE of his own people purely based on his own wounded pride and that the survivors of his previous war of conquest destroyed his bolt-hole of genetically engineered super-soldiers and died in squalor, rather than fuel his military machine.
So yeah, when he threatens to mind-control and then kill the Doctor if he doesn't take him back to Earth so he can conquer the planet using his super-powered mental domination powers to start a new galactic empire? I'm not really seeing the Doctor as being unmerciful, there. Especially since the Doctor did him several solids prior to that (not realizing he was dealing with Crystalline Space Hitler).
Most of the dudes the Doctor serves up there got several chances before the Doctor did what he had to do. I mean, there's a difference between 'merciful' and 'passive'. The Doctor doesn't LIKE to hand out the ass-kickings...but he'll do it if lives are on the line.