The main reason that you cannot reason with a JW, which by the way is talked about a lot in this forum, is called Cognitive Dissonance. Reason doesn't work when there is a disconnect that interrupts reason and logic.
The person could potentially cite the ideas of respect towards parents and parental obligations towards children. But even if they have no argument against your point, they will simply disconnect from the argument entirely and tell you that times have changed and God sends his laws to the GB now. It may be ignorant and lack logic and reason, but it is a circular argument that can't be argued against. They believe what they believe, and trying to argue with them won't change their minds.
Even when I couldn't argue a person's point (and that was all the time when defending my JW beliefs) I could always simply refuse to argue and put up that my belief is what it is and can't be changed. Then, even though I couldn't stand up for my own beliefs I would feel threatened with people trying to tell me that my beliefs were wrong. And that would make me think of all the instances where the literature and the studies talk about how Satan and worldly people will try to break you down. It did the opposite of what you seem to be wanting to do. It made me dig in deeper.
So, yeah, it could hurt. It might sew a seed of doubt or it might sew a seed of self-righteousness. I didn't leave because someone showed me the error of the beliefs. I left because I was shunned based on a rumor. I left because I personally saw inconsistencies in the way people behaved and the way they said they behaved. I left because the way people treated others was wrong. I left because I realized that no 'man' had the right to come between me and my relationship with God, and no man had the right to speak to me as though they were speaking for God, especially since they were getting it wrong.
A lot of people leave or stay in because of a lot of reasons that have nothing to do with JW doctrine and beliefs.
