I can understand why so may who oppose the slide into totalitarian nihilism, despair, suicide and self-damnation are so focused on discerning who is 'us' and who is 'them' - but the reality is that although there is a Them, there is not an Us - not in the same sense.
There is a Them united by their opposition to good, opposition to God. They can therefore police their boundaries, and they do.
But the Us is a collection of individuals. There is no boundary to police - and trying to make a boundary is destructive - tending to make Us into Them.
Christianity is in its essence about individuals bound by love, exactly like Families - it isn't about objectively definable groups/ organisations/ institution; except secondarily, contingently, always changingly...
Note added: One implication is that (here-and-now) if you want to run an institution, an organisation (including a church) that is not going to be absorbed into the single, evil, bureaucracy-media-plex; then you need to exclude Them... But you cannot achieve this by including only Us as defined... however. However Us is defined, it will - over time - come to include Them. 'They' can only be reliably and effectively excluded on an individual basis. (Here-and-now) Us must be a collection of individuals that cannot be captured by any definition that also excludes Them. It may (or may not) also be relevant that the attempt to exclude all of Them by a very restrictive group-definition will very probably cripple the institution, by excluding vital Us-es... This further implies the absolute necessity for individual judgment as primary: all Systems will lead to corruption.