I'm not sure where you see the insulting approach. It has been my experience reading Jar's posts that he is always respectful of the other posters and I didn't see any exception with his opening post.
I do know that some Christians sects don't consider other Christian sects to be Christians. For example I worked with some fundamentalist Christians who didn't consider Catholics to be Christians. They said that Catholics were all going to hell. What I never did figure out was that they also said that the way to salvation was to accept Jesus as your lord and savior. From what I can tell from going to catholic church and Catholic school in my youth is that this is precisely what Catholics believe. Of course they also pray to Mary and the saints but I think that god forgives these "sins".
Anyway, the short version is that I think that Jar was simply asking for people not to use the "you are not a real Christian" argument. Of course I could be wrong, it happens.