Trapp is one of the few WWI veterans in the battalion, so he presumably has experience both committing violence and having to deal with the psychological burden of it. He understands better than most what it’s like to cope with the fact of having killed another human being. This might have something to do with why he’s not considered SS material by Nazi officials—having been a part of violence, he makes no secret about being less than enthusiastic about ever doing it again. His two captains, however, are young SS men who clearly do have more enthusiasm for war and the possibility of violent action. As Browning explains earlier, only men who are both able-bodied and truly believe in Nazi ideology are allowed into the SS, so both Wohlauf and Hoffmann are presumably anti-Semitic and embrace the idea of getting rid of the Jews (either through deporting them elsewhere or even by killing them) to make more room for German expansion.