I don't view Fetterman as anywhere near that close to most folks here.
As far as where to draw the line... a really important question I don't have a good answer to. I'm not sure anybody has a good, consistent answer. But I think implicit in the idea of building a mass movement is reaching outside of the circle of people who are basically all on the same page, because that circle is small.
Is there an article about this with some more detail?