I'm glad to see this thread brought back up again, too.
The more I think about it, the more compatible I find mustachianism is with Christianity. For example, most Mustachians are aiming for a stache in the $900k-$2million range, and many find $1.2 million to be a gold standard, but definitely still not required. To the spendypants of the world, this may look like hoarding, but when you look at Boglehead types, who often require $2-3 million+, you realize that while mustachians focus on keeping calm and carrying on, other financial literates who don't care about frugality and intelligent living often get stuck in a cycle of fear and paranoia about not having enough money. But there really is no such thing as perfect security. I think if you're a Christian and you think that your money can save you from everything in the world, you are very much missing a key element of your faith. I think there is a lot to be said about taking control of our lives intelligently and trusting God for the things outside of our control. Besides, being content on $4k/month is way less greedy than the way most people live their lives, IMO. Greed would be saying, "I need to make $120k every year for the rest of my life because I need ALL OF THE THINGS!" But there are a lot of nuances here that I'm too lazy to flesh out, too (ie it's okay to keep working, of course)