There is a definite hierarchy within the prison system. Cop/ serial killers at the top and child molesters at the bottom (just below rapists).
Embezzlers are looked down on, too. Because they’re stupid. The crime leaves a paper trail.
I was in California prisons for over 25 years. That is pretty close to the truth. Guys that slaughtered women and children were not well liked either. Serial killers, not so much either, but I always felt they glorified cop killers, whether they made it plain or not. You are right, however, there is honor among thieves. It's weird, that the dregs of society have a code, but they do.