pbrow,
You, I, and everyone, have the personal right to decide to not communicate with someone based on whatever opinion we have of said person. That doesn't make anyone an extremist. If I believe someone in the neighborhood is a pedophile, I am entitled to shun that person and instruct my children to stay away from any contact.
However, it is a whole different matter when an Organization teaches and coerces its members to discriminate against others based on religious, racial, ethnical, or sexual differences. That constitutes a violation of human rights. That is indeed extremism. That is what the Organization of the Jehovah's Witnesses does. Ask the Jehovah's Witnesses if they would stop shunning ex-members if the Governing Body would tell them it was a matter of conscience and no one would suffer retaliation if he would decide to have normal social dealings with ex-members. I risk saying the vast majority would stop shunning. And that would clearly demonstrate that Jehovah's Witnesses do not shun as an expression of their free will, but rather, they take that extremist behavior in obedience to organizationally directed shunning.