Quote Originally Posted by Closet_Skeleton View Post
The doctor's actions in this episode seem kind of amazingly nasty, but they didn't bring up any moral questions at all. Tennant angsted about doing things that were no way near this bad.
True, The Doctor doesn't normally resort to such measures, but in this case I think he figured he didn't have much of a choice. The aliens were doing significant harm to humanity, and this was the best chance to stop them. Also, he did give them a chance to run.