Reality check: It's incredibly hard, if not impossible, to build real communities online. People just don't have a true stake in it. There's no chance of bumping into that other person at the local coffee shop. No concerns about having to actually work together with someone they dislike. No real coexistence or cooperation. These limitations cut both ways.
The naive response is to boot individuals that don't "fit in." That leads to the problems mentioned in the article. An alternative response is to erect hurdles that restrict access only to those deemed worthy. This has a deleterious effect on external perception and fosters an internal sense of elitism.
But seeing people advocate for these solutions isn't a sign of the end, it's the natural and inevitable response to concerns of growth and change.
This happens in the real world, too. Look at home owners' associations, community covenants, and gated subdivisions. Each an attempt to create a tangible (financial) stake for members, provide recourse in case someone doesn't fit in, and limit who can enter in the first place. These aren't bad in and of themselves, but only rarely do they help produce a true community.
I don't know how to address these issues. The real world examples, where much more is at stake, lead me to believe that there may not be a clear cut solution. But we can't survive by closing our borders. In the long run, the isolation would hurt us far more than a disruptive Outsider. Instead, we need to find ways to actually engage the folks that stumble into our fold.