Let me preface this by saying that I don't have kids so its entirely possible that I just 'dont get it' but I see this as a common tool in movies, books etc.
A parent has a kid that is in danger. The bad guy uses this to make the parent do something terrible which often involves killing tens, hundreds or even thousands of innocent people or to advance a plan that would result in an evil dictator taking over, entire people's being enslaved\tortured, millions killed, or humanity destroyed. Would parents really be willing to be directly responsible for thousands or millions of other kids dieing so that their child could live? It would be one thing if the person was a megalomaniac or evil character but that is often not the case
A parent has a kid that is in danger. The bad guy uses this to make the parent do something terrible which often involves killing tens, hundreds or even thousands of innocent people or to advance a plan that would result in an evil dictator taking over, entire people's being enslaved\tortured, millions killed, or humanity destroyed. Would parents really be willing to be directly responsible for thousands or millions of other kids dieing so that their child could live? It would be one thing if the person was a megalomaniac or evil character but that is often not the case
