My guess is that a line of thought regarding the nature of the motive made that jump possible:
The group, like extremist groups of any ideology, seemed to be pretty "in or out". Either you are part of the "tribe", or not part of the "tribe". Non group members were probably then classified as "trustworthy" or "enemy".
The line of thought seems to have been that they were defending the children from outside "enemies". Unless stopped, these enemies would harm members of their group. Group members must be defended at all costs.
In short, the crime was not presented as a crime, rather as a "need to defend". This likely made the jump far easier than if it were presented as: "OK, I started selling drugs- now I need your help to murder two rival dealers..."