Call me sadistic but I think they should flood the internet with "bomb recipes" that are specifically engineered to be so unstable they blow up as soon as you mix them.
It wouldn't have to blast many before every wannabe terrorists gets wind and doubts every bomb-recipe they find online. Or at the very least search so hard for confirming the bomb recipe that they draw enough attention to be caught. As deluded and selfish they are, I don't think even they are deluded enough to think they will get their divinely appointed 72 prostitutes it they blow their hands and eyeballs out.
I don't know how legal that is. I mean it is illegal to make explosives for murderous purposes, would it be illegal to con those murderous criminals into maiming/killing themselves?
I consider it consistent with self-defence, it directly prevents them murdering others, though not an immediate threat if undetected it is an inevitable threat.
It's fair game, if you don't want to get tricked into blowing your face off, DO NOT try to mix explosives in secret! Only terrorists on civilian targeting operations do that!