This way I promise no one will join the rebells. Why would anyone join the rebells just because their families are slaughtered? That's absurd.
(Irony.)
There comes a time when YOU would strap on a bomb belt. Just imagine that They killed half your family and then goes on telling you they will continue doing it...
I don't think this is quite enough to push people over the ledge. If what killed half my family is someone who does not try to justify his actions morally, someone who I can therefore morally compare to a tiger or bear, I wouldn't strap on a bomb belt. But if the killer tries to tell the world he's eradicating evil, and the world high five with them, ...
It's not that hard to imagine - after 9/11, people did enlist themselves to go and start shooting at others, sometimes with the consequence of dying themselves, believing it is for the greater good.