Imagine your child is kidnapped in a world with and then without bitcoin.
Without: In order to ask for and recover a ransom... there needs to be a physical drop off, or trackable transaction which can allow for the recovery of the child or the funds. Many possible situations must be contemplated by the criminals including... stings, tracking embedded cash, set-ups, etc. etc. Making the job of the criminals difficult.
With: Simply kidnap who you want, demand bitcoin. Kill those who do not comply, collect from those who do.
From the eyes of a criminal, there's no difference. In those African states where kidnapping is relatively common, organizing the recovery of a ransom isn't a problem. The criminals know too well that as long as they keep one hostage, the person paying will not take any risk which could endanger the life of the person kidnapped. Hey, even governments with all their power and armies pay ransoms!