-admittedly semi-justified reasons-
Semi-justified? They were cultists of a preacher preaching a message of extreme intolerance to metahumanity, who were also starving kidnapped, magically mesmerized metahumans out in a confessional area (and had, in fact, killed all but the lady we were there to rescue in this fashion), their priest had sinister fire spirits guarding his body at all times, fell upon a dagger and sacrificed himself to become a big flaming pseudoangel thing.
In the meantime, the cultists themselves continued their ritual mindlessly, bringing a coffin with two children in it to the altar (at no point did they try to get on the ground, run away, surrender or even say as much as a polite "don't kill us" as well as fell upon well-armed gunner robots en-masse, trying to beat it down with their bare hands and eventually succeeding). One of them got shot dead, and another just jumped over to keep hauling the coffin. Let's face it, these guys were pretty damn insane and probably actively harmful to society, at least while the priest was still around, regardless of whether their intended highly suspicious-looking ceremony was ultimately harmless or not.
Of course, their tortured souls are still going to populate the area for years to come, and the magic in the area's going to get corrupted over the years by their psychokinetic presence, to say nothing of the rift that got ripped open over there, but hey, can't win 'em all.
We did also hand the kids over to a new home, which happened to be the seemingly reformed pollution spirit who used to be terrorizing a neighborhood but now happens to lead the spirits of Middlesex Fells Reservation in a bid to make the locals respect the land again (all made possible through our efforts). This will probably turn out not very well for the Greater Boston area, considering the forest is becoming... kinda primeval and forbidding in that area, but hey, at least the spirits there'll appreciate it a lot!