Just running out, I'll be back later to argue with you about how I wouldn't argue about absolutely anything.
"I came in here for an argument!"
"Oh, sorry, this is abuse!"
No it doesn't work that way. If we for some odd reason started throwing terrorist's families out of helicopters (can't believe I'm actually having this conversation, but anyway), you'd radicalise thousands upon thousands of other people. It'd make the situation worse to an astonishing degree. A PR fantasy for extremists.
You're talking about the spillover effects. I'm talking about actually deterring the terrorists.
If the terrorists all cared about their families more than the cause, this threat would deter them. In general, they don't, so it wouldn't.
The spillover effects would be irrelevant if the threat actually deterred the terrorists. In some cases, it is our actions that denied the terrorists families and led them to become terrorists.