My pleasure, really! Ruth Morris and Kaba are, for me, the two insisting the most on the link between first nations practices of restauration and possible ways to start an abolitionniste strain from there, if you're interested in these..
As for the movement in general, it started to grow in the 60's. Mainly driven by professors of law and critical criminology, on the one side, prisoners movements and unions on the other side. A great deal of anarchists, a lot of religious people, a few moral radicalists. Many had a common experience of nazi camps. That may be too simple of an explanation, but some of them explicitly state that to account for their interest in prison and hatred for the penal system.
It was, but actually, gatekeeping as you defined it fits the kind of situation I broadly wanted to refer too. This example is a little extreme, but yeah. Thanks for the definition, btw!