Because, although the group you seek to describe is secular, their defining characteristics have strong religious overtones, you might consider the following:
TRUE BELIEVER noun:
1. a person who professes absolute belief in something
2. a zealous supporter of a particular cause
See, Merriam-Webster “true believer”
Devotee noun: plural noun: devotees
a person who is very interested in and enthusiastic about someone or something.
"a devotee of classical music"
synonyms: enthusiast, fan, lover, aficionado, admirer;
"a devotee of rock music"
• a strong believer in a particular religion or god.
"devotees of Krishna"
synonyms: follower, adherent, supporter, advocate, disciple, votary, member, stalwart, fanatic, zealot
see, Google.com “devotee”