You say "cult" like it's a bad thing.

Seriously though, using a term with negative connotations is not a rational approach t begin with. Like asking "is this woman a slut?". It presumes that a higher-than-average number of sexual partners is necessarily bad or immoral. Back to the cult thing: why does this term have a derogatory connotation? Says wikipedia:

In the mass media, and among average citizens, "cult" gained an increasingly negative connotation, becoming associated with things like kidnapping, brainwashing, psychological abuse, sexual abuse and other criminal activity, and mass suicide. While most of these negative qualities usually have real documented precedents in the activities of a very small minority of new religious groups, mass culture often extends them to any religious group viewed as culturally deviant, however peaceful or law abiding it may be.

Secular cult opponents like those belonging to the anti-cult movement tend to define a "cult" as a group that tends to manipulate, exploit, and control its members. Specific factors in cult behavior are said to include manipulative and authoritarian mind control over members, communal and totalistic organization, aggressive proselytizing, systematic programs of indoctrination, and perpetuation in middle-class communities.

Some of the above clearly does not apply ("kidnapping"), and some clearly does ("systematic programs of indoctrination, and perpetuation in middle-class communities" -- CFAR workshops, Berkeley rationalists, meetups). Applicability of other descriptions is less clear. Do the Sequences count as brainwashing? Does the (banned) basilisk count as psychological abuse?

Matching of LW activities and behaviors to those of a cult (a New Religious Movement is a more neutral term) does not answer the original implicit accusation: that becoming affiliated, even informally, with LW/CFAR/MIRI is a bad thing, for some definition of "bad". It is this definition of badness that is worth discussing first, when a cult accusation is hurled, and only then whether a certain LW pattern is harmful in this previously defined way.