I think you're reading more into the OP than is there. Family relationships were not the particular subject; no relationships of any specific sort were the subject. Relationships with "everybody who he doesn't consider to be a rationalist" were not the subject. The last may have been suggested by the context of the Columbus Rationality Meetup, but is there anything more here than "other people persuading each other of things I disagree with"? That does not make a cult.

The social default is that you don't cut of relations with members of your family even if you don't draw value from those relationships.

In some of the more unpleasant parts of the world, perhaps. A better default is "you don't cut off relations with members of your family unless for very strong reasons." Some people do actually have such reasons.

With the inside view you always can find reasons.

I spy invalidation! A telling sign of a cult, undermining the members' ability to trust themselves!