I don't think the article proposes that a community should not accept new members. On the contrary, it critiques the breaking of communities.

Migrants or refugees have to find a new community because their old one was broken for whatever reason, be it war, financial troubles or something else. So in that case, that first breakage of community should have been prevented and the community preserved.

If anything it's well known that migrants tend to build communities as well as high-skills "expats".