Doctor Who: 10 Worst Things The Tenth Doctor Has Ever Done
8. Various - People Into Weapons
"You take ordinary people, and you fashion them into weapons" - Davros.
And when you think about it, that's so true. It's a running thread throughout the Doctor's life that he has major impacts on people, but how many put their lives on the line because of it? This is quite notable in the Tennant era.
Travelling through Time and Space you are going to across plenty of people, but to leave such impressions that they lay down their lives is significant. It often comes as a result of the Doctor not willing to go all the way to stop someone. For example, take Luke Rattagan, he wiped out the Sontaran invasion fleet. He did this because he felt he had to make things right for being used by them, but its also arguable he knew it wasn't in the Doctor's nature. Thus not getting blood on his hands.
This moment comes to a head with the aforementioned speech by Davros:
As the video shows, the most notable examples of this in the Tennant era is the Children of Time. But also, we have seen the loss of Astrid, Luke Rattagan and Harriet Jones, all dying basically trying to do what the Doctor does.
Whilst directly not his fault, that's quite a dark legacy.