There is a challenge in isolating extremists while not isolating (and, indeed, productively engaging) the communities from which members are radicalized, and quite often brute-force efforts to isolate extremists (especially ones keying on race, nationality, and religion) end up isolating the feeder communities with the extremists, which is about the worst possible outcome.
Honestly this is a terrible precedent they have here. I am surprised they are doing this (if true and hence why I questioned the entire story) because it puts them at a disadvantage in future cases as far as 'why didn't you stop xyz domain registration that is now responsible for my child's death after I wrote to you and put you on notice'.