Someone tried every other thing to end, The Time before making that horrific choice.

Sometimes, The Doctor wonders if his Seventh Incarnation tricking Davros into blowing up, Skaro was what started The Time War. Though, didn't help. That is for sure.

The Doctor's face is hard still but also determine. In strong tone remarks, with a bit of a growl remarks;

"I'm not you."

Then silence. His voice is quiet, disgusted, and ashamed. "I didn't have any other choice."