Sure, it's logically valid. It reduces to: P1. A. P2. B. C. A and B. Depends what you mean by fallacious. It's garbage in, garbage out. The conclusion is only as good as the premises. Refer to my more-concise version, above. If A or B is false, the conclusion immediately collapses in a heap. It's not the logic that is at fault, it's the assumption that P1 and P2 are truths in the first place. ---- Edit: Reading down, I see that Sarkus got to this before I did, so please excuse the repetition.