We are part of the Christian church, and I feel like our relationship with God simply gives us clearer goals and motivations for Mustachianism.
Obviously, 'hoarding' in the sense of greed is wrong, but saving for the sake of freedom can be right, if the freedom includes the freedom to be generous, serve others, minister, and give of yourself.
Part of my desire for FIRE is not neccesarily to fully retire early, its simply so that we have the flexibility to do things like move, take trips, take on poorer paid jobs, write, teach, and minister to whomever and wherever we feel led, regardless of cost/circumstance. We also love giving to worthy ministries and causes, and we can choose to care for those less fortunate and those that are part of our church family, because we are wiser than many with our money.
Of anyone, a mustachian with a strong faith background will likely find it easier to avoid being 'taken over' by the money saving aspect, because one is consistently reminded of the purpose and motivations of life behind it...living both joyfully (as God intended) and generously (as God intended). Contentment is a huge factor, and knowing what true wealth is too. Faith shouldn't ever be annoying, boring, or stuffy....faith is persistence, zeal, risk-taking, and action....which are often things associated with the Mustachian way!