Now, explain the term "extremism"...
Well, someone needs to because that isn't it ...
Is it because the word does double duty that some people get confused?
For example, you could say that someone is extremely religious but that doesn't mean that they are automatically an extremist as most people would understand it (they might be, but it's a different use / meaning).
You can be extremely [anything] without necessarily being an extremist.
For me an extremist is someone who's willing to harm others for their cause.
Now I know people will argue that JWs do that, but do they ... really? To the same degree that real extremists do?
It's like lumping physical assault in with verbal assault and then claiming that someone saying something mean therefore physically attacked you. I don't think most people would believe they did.
he would shun me completely
That is an assumption you are making. You can only say what he has done, not what you think he will, when using someone as an example.