Tom Sheepandgoats has written an excellent post defending disfellowshipping (more popularly known as shunning) in the Christian congregation.
So it is with Jehovah's Witnesses today. They could not be more unlike in personalities, backgrounds and talents (besides the factors already mentioned) yet they enjoy unshakable unity. God's spirit makes it possible.
We're zealous to safeguard this unity. When a person leaves JW tenets, he begins to lose the thinking that makes such unity possible. Some lose it instantly. More
often, it happens over time. But it does happen.