I'm convinced JW's are under sooo MUCH brainwashing and fully indoctrinated that their brains are disabled. They will never analyze or question any beliefs. It is all about the emotions, their brains are literally paralyzed. They cannot do any critical thinking. They will never question or debate any ideas with logic, coherence and facts. It's all about circular reasoning on flawed data/logic that leads no where. Their arguments will always be biased on the doctrines imposed by the Watchtower.
At any moment where they may start to think or question something, mental triggers will kick in to induce guilt and fear, this starts a chain reaction to shutdown the brain. It's actually a very basic formula. They have been literally programmed like a machine to stop working when something is considered a threat to their survival. The routine is simple; induce emotions for everything and shutdown any critical thinking abilities. The brains are essentially wired to protect the Watchtower identity (self-sacrifice, slave mentality).
Emotions are basic survival instincts that prioritize based on the extent that something could pose a threat to a person's life. Anything that can endanger your survival has a higher priority. Anything that causes fear will be avoided at all cost. That's why the BORG will build the concept of a "spiritual counciousness" that guards against any ideas that may be considered a threat. They basically protect those mental triggers and reinforce the guilt and the fear with shunning, and other cult practices.
They have literally installed a "trojan horse" in your brain that acts like a firewall that blocks the ports that communicate with the brain. This analogy may be the best way to illustrate what effect they have on a person's abilities to think on his/her own. They destroy that ability to trust in your own belief system and to constantly fight it.
They like to use the concept of the heart (based on emotions) as being a lot more important than the brain. But they will tell you, the "heart is treacherous", not to trust it. Basically, they want you to get rid of your own thoughts...and only accept what we they tell you!
From my personal experience and seeing others, you need a major shake up in a person's life that could cause a reboot of the brain, in order to start thinking on your own and to start questioning your belief system with logic and research. You have to start from scratch. This is the only way to bring down the firewall that could enable the brain to start functioning again.
Any explanation from the Watchtower on anything will be sufficient to accept their beliefs, it doesn't have to make sense (e.g. "blood fractions", "generation overlap", etc.). This is the case for the great majority of witnesses, they will keep going without thinking. They encourage that behaviour, the acceptable way to gain status and to have a sense of belonging and purpose within the cult.
The cult is all about denying yourself as an individual with free will, getting rid of the self. That explains why birthdays are not allowed, anything that excels the self is forbidden (e.g. masturbation, etc..). It's all about the collective (the group, the leadership), the great fellowship around the world, God's people on earth and not about what you think, but rather what is imposed on you from the group.
This is how I can summarize the cult mind control and how they've managed to have so much control on millions of people.