Validity: The passage explicitly states that the four-case argument (covering the deterministic case) combined with Pereboom's argument (covering the indeterministic case) forms "an important part of a detailed and influential skeptical perspective," which clearly entails the extracted argument that together these premises support skepticism about moral responsibility.
Confidence: The overall skeptical argument is clearly entailed by the combination of the two sub-arguments described in the text, though the passage is partly expository.