The only reason for the DFing thing is Control. It is on extremely shaky ground as a practice if you read, IN CONTEXT, all the Scriptures they "base" it on.
But it is beloved by the G.B as a control technique because the pull of family is strong, and it more often than not stops any of the TTAT getting to the J.W's, even people like me, merely faded/inactive, refrain from discussing religion with J.W's, because a DFing is always a threat. Control, Control is the G.B's Mantra.