Cult and mind control are both accurate descriptions, but can be counter productive and taken with offense. Other terms to use are "high control", "undue influence" and "coercive persuasion."
Teenagers are perceptive but also vunerable to these types of groups. Rather that discuss the Watchtower being a cult, continue as you have and highlight the techniques that make it one, and how there are manifest in other groups. You will do him a favour not only to leave the Watchtower, but also to learn how to avoid similar groups. Lifton's criteria are the foundation to any discussion, but also a bit difficult to understand, so try to make it more obvious by application to other groups, including religious, corporate and political.
Multi-level marketing companies are very compelling for young people trying to make easy money, and so similar to the Watchtower structure that would be a great discussion with your son. The sales pitch always includes the following points.
- Do you want a better future
- Would you like to remove all your money problems
- Do you picture yourself with a yacht in a paradise island
- Do you want to belong to a special family of like minded individuals
- Wouldn't you love to belong to something that improves the world
- What we have is the best product of all that are out there
- You need to make sure you use our product and not others
- You need to talk to everyone you know about this to build your network
It is easy to see how these comments apply equally well to a Usana, Amway or any high control religion, and you will hear them at almost every meeting.
I would keep your wife out of this for now, as you don't want to start a battle between the two of you for your son's allegiance.