The common thread is "comprehension." You can't comprehend why a person would desire performing oral sex on their teenage daughter, just like I don't comprehend why a disgruntled german man would set in motion plans for mass-murder. Just because neither you nor I understand the terms of each situation, doesn't mean that those things don't or didn't happen. They are not on the same level of atrocity by any means, but they serve the analogy just fine for my tastes.

That good enough for you, Susie, or would you prefer it if I had Big Bird sing a nice song about it for you?