I think the financial aspect of your lifestyle can be defined in terms of a continuum, with ERE/MMM on one end, and the consumerist debt-laden over-spender on the other end. The middle is probably someone who got a "C" in Personal Finance 101: he isn't spending more than he makes, but could stand to do a fair amount of optimizing.
tomsang, I get the impression that you're like me, in that you're somewhere between MMM and the midpoint, the 25th percentile, so to speak: doing far better than the typical first-world middle class individual, but still not living up to the standard set by MMM. Clearly there are different opinions on the "philosophy" of Mustachianism. Some will say you're already there, since you're saving so well and living in a conscientious manner. Others take a harder line on the issue, and want you to be nearly a clone of MMM before you're truly living out the philosophy.
I agree that it can be alienating to go "further down the rabbit hole" of Mustachianism (to use the Matrix analogy). When I think and post on these things, I like to start with the
How to Go from Middle-Class to Kickass post. My spending is around twice that of MMM's... but it's still far less than MMM's former colleagues, and I'm lucky to make a considerable wage---enough that my savings percentage is definitely "MMM approved". But the savings rate is really only one facet of the overall MMM lifestyle.
I see some signs of relationship straining with my closest friends. They also have high incomes, but take the "your lifestyle should reflect your status" attitude. For example, luxury cars. We got into a somewhat heated argument about how wasteful they are. I was looking at downsizing and going more fuel-efficient; my friends think I'm ridiculous for not getting a luxury car. As others have said, it's a matter of values. They value the "finer things" in life, even if it means working longer or even leveraging yourself; I value getting FIRE sooner than later.
That story might make me sound like I'm living the Mustachian life. Clearly, my friends are candidates for the "Antimustachian Wall of Shame and Comedy". But if you pick the story apart, so am I. Though I'm going for a small, fuel-efficient hatchback, and paying cash, I'm still looking to buy new, and indulge in a few upgrades. And why am I buying a car anyway, why am I not using my bicycle for 99% of my transportation needs?
I found great comfort in the book
The Millionaire Next Door. It seemed to be largely about people who were more like myself: that is, recognizing the value of saving and investing, and generally living below one's means. But by and large, I don't think these were "extreme frugality" types (except maybe the Scottish). I suspect most fit in the 25% percentile I suggested in the continuum discussion above.
Last year, my wife and I took a semi-expensive adults-only vacation with said friends. It wasn't crazy expensive, but definitely and indulgence, and quite unlikely to be "MMM approved". We had a great time. Part of my justification for the trip was that, with kids, I really won't have opportunities to do these kinds of things very often. But while there (since I had more time to think than I usually do), I found myself thinking about Mustachianism, and what makes me happy. Yes, I want FIRE very badly, and the best way to get there is to reduce costs and spending to a minimum. But what happens when sweating every penny becomes an obsession? If it's just saving for the sake of saving, then is that what I really want out of life? Well no---it's saving for a longer-term, bigger goal. But if reaching that goal means I have to give up these rare opportunities to relax without kids and enjoy the company of friends, is it worth it? (And in case I mis-characterized my friends: yes, we clearly have some drifting values. But still we share a number of values, and more importantly, don't take ourselves seriously enough for the differences to matter. We can disagree, and maybe even get a little tense, but 10 minutes later we're all laughing again.)
While some friction between friends does occur, I can thank my kids for helping smooth things out. Without kids, I think my friends would be more often trying to pull me into spending money. But with kids, we barely have time to get enough sleep, let alone do all this stuff that requires money. Increasingly, the gatherings with friends are increasingly low-key, and more of the lines of "let's hang out at someone's house and just take it easy for a few hours."
I'm living in Chicago now, as are the high-income friends I've mentioned. I'm a transplant to this city, though. In my hometown, I have friends and family of much more modest means. I'm only here for the high-paying gig, and when I hit FI, it's back to my hometown. This is in line with what other people in this thread have suggested: it can really help to literally move in order to better surround yourself with more like-minded people. And I think you really have two options: surround yourself with other rich-but-frugal Mustachian types, or people who simply don't have the means to live "above" MMM's lifestyle. Either way, you fit in. :)
I also believe that moving back to my hometown will further help me reduce expenses---but then again, maybe it's just a dangerous rationalization for letting my expenses be where they are now. If nothing else, housing costs will all but vanish (I have a mortgage now, but will own outright after FIRE). The number of times my Chicago friends will be able to rope me into spending money will effectively be zero---spending money with them will now be a special occasion, rather than a regular weekend thing. Restaurant selection will shrink dramatically, so the temptation to eat out will be lowered. Living near both sets of grandparents means free babysitting. And I'll have so much more free time to DIY all the things we now pay for to save time.
As evidenced from this post, clearly, I favor the "soft form" of Mustachianism; I haven't fully drank the kool-aid. I still maintain a number of "typical" middle class lifestyle behaviors, but I do so conscientiously (insofar as my own values are concerned), and spend far less than I earn. And I still keep an eye out for waste and areas where we can save more.
I think that, loosely speaking, with regards to Mustachianism, people fall into three camps: (1) hopeless, (2) natural, and (3) transitioning. The first are the ones who'll never get it; these are the haters that show up spewing vitriol whenever MMM gets mainstream exposure. The second are the "natural" Mustachians, the ones who have always, instinctively lived a life similar to MMM's. The last group are probably the biggest group, those who are not natural Mustachians, but who want to adopt a similar lifestyle. And I'm sure within this group there's still a fair amount of diversity, from those that just need to make a few little tweaks, to those that need a radical lifestyle overhaul. But in either case, you have a transition, and the dynamics that encompass the transition can make it smooth and easy, or painful and difficult. A major factor in the transition is one's spouse---that's got to be one of MMM's FAQs: "I want to be like MMM, but my wife/husband doesn't, what do I do?" The fundamental question is, what happens to my relationship to someone I love when our values change? Framed that way, the question applies not just to one's spouse, but his family and friends as well. In the worst case, there's divorce/disownment/ended friendships. But more likely (and hopeful) is probably some middle ground or compromise. Which do you love more, your wife or Mustachianism? Assuming the former, you'll probably relax your definition of Mustachianism a bit to save your marriage. Hence, the continuum. Stated another way, depending on how far you want to take it, it's really a character-defining situation.
My last paragraph made me think about this question in a more general sense: what are your biggest sticking points when it comes to transitioning to Mustachianism? Is the numbers/math? Is it giving up convenience and luxury? Is it the effect it will have on your relationships? Is it simply the fear of getting out of your comfort zone? The answers, and the degree, will of course be different for everyone.
Whew, that got pretty long. I'll be happy if anyone bothered to read the whole thing. Even happier if anyone got anything out of it! :)