Weart examines every recorded instance of violent conflict among democracies and comes to the remarkable conclusion that they have never gone to war against each other. Carpenter engages in sophistry. He poses a hypothetical and treats it as a fact. Rummel's point was, quite obviously, about regime types in the aggregate. He could have done something like compare the extent of violent conflict between two countries while they were under different types of government, if he had wanted to be persuasive.
Carpenter is obtuse.
Furthermore, covert actions are by their nature secretive and non-democratic, and so, according to Rummel's theory on democracy and peace, we should even expect them to be violent. But even here Carpenter misses the point. One of the impressive features of Rummel's research is his discovery that democracy is a whole cloth, with interwoven strands of nonviolence and peace at all levels. Rummel's theoretical work is very important and should have been engaged. It was not.