"It WILL fuck things up more." Dean said with absolute certainty. "It's not a possibility Claire, it's a certainty. It will shatter all of those pieces into smaller ones until there's nothing left of you to get through the day or be the person you want to be." The words were truth, but they were also woefully inadequate. Dean knew that you couldn't tell someone what happened when you stopped hurting and started living for lashing out. It wasn't really living at all. She had her first taste of it tonight, when she snuffed out something that wasn't even human anymore in a more gruesome manner than possible. He knew without a doubt that if he let his Claire torture Sylar, what came out of the room wouldn't be the same person as before.
That was not to say that he wouldn't love her. He would always love her, as she had always loved him even when he was at his lowest point...but he didn't want to see her like that. He would do everything within his power to keep her from bringing herself down to that lowest of low points.
"Making him scream will make you fall apart completely, it will make you sink down so low that you don't want to be around me or Ben or anyone. It will give him one more piece of you, one more win, and I'll be damned if I let him have that. He's not fucking worth it."