There is no link (yet) so I can't fully evaluate his arguments, but from what you said, I have a few comments.

I absolutely think that there is a difference between how a theory is justified and how it is put into practice. For example, I am fully justified in hugging my little brother. However, if I hug him so tight and for such a length of time that he dies from it, then I have abused my ability to hug.

I am on the fence about the justification of capital punishment, Jesus Christ and all his banter about forgiveness and a lack of instruction on the state level. However, even if it is justified, Dave has a litany of examples where the execution was botched or people who were going to be killed were exonerated. Because of those flaws in the system, I am against the death penalty, although it might be justified.