becoming a JW is a voluntary association.
I don't think people who sign up to become JWs truly understand what shunning is all about. Sure, they certainly mention it, but never really go into the details, or when they do, they do it so briefly that it is difficult to grasp its true nature.
They make it sound like the people being disfellowshipped are truly bad people, on par with murderers, adulterers, violent alcoholics and lying deceitful cunning sinners that actively want to harm you. They make it sound like a good thing, for your protection! They dehumanize them. As for the others, well, its only a brief temporary disciplinary measure; they’ll be back in a year or so.
Newcomers generally fail to grasp that disfellowshipping is not about the sin, its about the adherence to the group membership. Consider that many people get disfellowshipped for some sin they eventually stop practicing, and yet, their shunning continues to the end of their lives. They are not shunned because of what they did, they are shunned because they did not try to get back into the group. And so, the group simply takes the position that the person must still be actively practicing some sin or another. For instance, think of all the young ones who got disfellowshipped for practicing fornication and have since married; yet, they remain shunned by their family.
We can also doubt that new commers grasp the following possibilities: When you get baptized today, you agree with several teachings and practices that will change over the years to come. You may not agree with some of those changes and refuse to remain a JW. Or perhaps, as you study into greater depth the history of your religion and the basis of its teachings, you may choose to leave the group. Then again, you will be treated as a relentless sinner, a perpetual evil doer and loose contact with all of your JWs connections (friends and family).
Absurd situations like these will happen because all these people will not have the right to make this assessment for themselves, or to review their position over time. They are ordered by their religion to do this and as a result, the majority of them entirely avoid the process of thinking and considering the matter; there is no options, only the one that is ordered.