I go on alert whenever anyone quotes a dictionary in this kind of
context. Dictionaries are always behind -- they cannot capture all
usages and they cannot be kept current. Words have connotations, and
those connotations can not be ignored when convenient.
Like it or not, "cult" is now a pejorative. If you don't want anyone
to hear a pejorative tone, you will have to choose another word.
If you meant to characterize extropianism as a secular religion, you
could just say that. Perhaps for some people, extro-trans-humanism is
a low-fat religious substitute (Religion Lite(tm)).
This belongs in the FAQ if it's not there already, it's a hardy
perennial. My take is that non-religious people use a lot of memes to
fill the niches vacated by traditional religion, and there's nothing
wrong with it, especially if they see it for what it is. There is of
course a trap to fall into, of bringing over blind faith, misplaced
zealotry, and other baggage from religious conditioning.
-- firstname.lastname@example.org (Freeman Craig Presson)