The whole group of Ren could be a sort of radicalized or idealistic break-away faction complicating an already dangerous dynamic.
In the NPR version of Star Wars, there’s a second layer of dishonest military leaders who hint that they could break off from the Empire and further muddy the Empire/Rebellion relationship. They don’t act on it, but they are aware of it and you get the feeling they’ve weighed the possibility.
Maybe The Ren are a similar group, but didn’t err on the side of discretion. They may have decided to take matters into their own hands. Not at all unlike modern day geopolitical relationships.