If some random person tells me that their belief system compels them to perform demonic ritual murders of the innocent, any cite from any religious tome or talmudic scholar or graven tablet doesn't debunk or refute what they are saying.

You can certainly make the assertion that their belief is a schism away from whatever the core doctrinal positions are, but thats besides the point that they still assert a right to perform these murders. Maybe they are a radical offshoot faction, maybe they are lying, or being deceptive? Are they threatening all this monstrous activity out of a desire for attention, or blackmail, or because they are insane? Maybe they arent at all informed. Does it really matter when they are threatening killings?

Surely every society has the imperative to purge itself from threats to its proper function as a priority. Have all the debate you want after the fact, go crazy once the threat has been dealt with, negated, or relocated to where it no longer is any danger.