Don’t know about the halachos of mesirah other than the idea of killing a moser not applying nowadays. But furthermore, if they were in fact snitching on unsafe shuls and weddings, it certainly doesn’t sound like classic mesirah to me. Based on medical consensus they likely have saved multiple lives, while classic mesirah brings on criminal charges, prison, death, etc., none of which is applicable here.
Now the irony of labeling someone as a sinner in order to transgress multiple serious aveiros themselves only strengthens the argument that they simply beat them up because they are bullies and they hate them, pure and simple. Any justification for the radical jihadists is abhorrent.