Draco understood what she was feeling, probably better than she did. He'd had time to come to terms with it in himself, after all. Not only in his past, either - right now, what he really wanted was the control she was feeling glad for, wishing he could do something to the bastard she'd killed. If he hadn't already been dead at Pansy's hands, Draco would have killed him, and much less cleanly, too.
"It's that last part that makes it possible to do it more than once," he said, voice quiet. "If you concentrate on that, and try to shut out the rest. Not that I think that's what you should do." He was silent for a moment. "Concentrate on the fact that you care, even if it's difficult. It'll be better for you, in the end."
He hadn't even thought once about the people who were left behind when he killed, and didn't want to start thinking about it now. Everyone's lives were at stake in some way or another, everyone had to come to terms with the fact that their loved ones might die. He did everything in his power to keep those people safe, and if his will to do so superseded someone else's, well. That was just too damn bad.