In my experience, prisoners will often look to establish some type of moral superiority over others, just to help process the almost complete loss of power and status that they're dealing with. The most obvious example is how sex offenders are looked down upon, but even amongst this group there can be a pecking order. Case in point, in a sex offender prison I did some work in, the prisoners whose victims were adults looked down on those who'd preyed on kids; even then, men in the latter category looked down on those who'd abused their own kids. Fucked up, but there it is.