I'm not so sure Mustachianism requires a lot of faith. It's mostly empirical observations and deterministic mathematics (along with stochastic outcomes like stock market sequence of returns). I can, for example, ask 100 early retirees how they achieved ER, how they invest, how they feel, etc. They can provide me with evidence of how they did it and what it feels like. I could even get audited financial statements to prove they are actually FI.
In contrast, I can't ask 100 people who are in heaven about their path to ultimate salvation and bliss, how they achieved it, and how they feel. They are dead, and as far as I know, there is no reliable way to speak to them from the afterlife. Whether they are up there floating around is a matter of pure faith since there is no way to falsify the claim.