I think this shows another glaring split between gamers. Those who want their games to be nothing more than in-person video games and those who want their games to be more than that. I don’t see making decisions “conducive to the theme of the campaign” as “trivial personal preference”.
First off, and directly to the point- your situation falls under the "MORE SERIOUS PROBLEM" category here. I don't know of anyone at this point that is arguing otherwise.
As to the other condition, I see where you may have gotten confused. I had originally separated those concepts as reasons behind banning things, but due to my recent experience with my very own
Trivial Personal Preference DM™, I combined the concepts in a later edit. Our group can not play Aasimar, Halflings (they are mutated to rat-men), Orcs (half-orcs get a pass so it's not mechanical-based restrictions), and a few other races. At that point, even though it is conducive to their homebrew world, it is stepping on player concepts at that point for very little gain. I can't get inside their head, so I'm unsure if pruning the race tree fits into their fantasy vision, or they just don't like halflings*, etc. I'm assuming a little of both. I personally decided it wasn't worth quitting over even though I think it's stupid. I hate homebrew worlds. Hire a staff of authors and artists to flesh it out some then publish it on a blog so your players can access it at least. That's my own trivial personal preference that you can cash at the bank (I have overdraft protection). Still, it's not worth kicking up dust over.
DM fiat can be trivial. Show me a DM without trivial preferences they put in their campaigns and I'll show you a strict published content DM. (even then there will be ways they run it that are unique to them) Trivial doesn't automatically slant pejorative† unless your bias in not accepting everyone at the table to agree with you about it bothers you. My character concepts are trivial to most everyone not at the table and some that are. The same goes for your opinion on how to run your game whether you recognize it or not. Use a different currency & exchange rate for every city in the region? Trivial‡. Bother with exchange rates, but not encumbrance? Still trivial. Cause bowstrings to break 5% of the time on critical misses? Triv- no, that one is just flat-out dumb. Not trivial
to you of course, not to the players
happy with how you envision your game world (probably) -you likely aren't taking a
scalpel hacksaw to the PHB on races like mine is. But you do seem to have an issue with a couple of friends about your stance on munchkins. Not saying THAT is trivial, in fact, that's okay- you have Rule 0. You've obviously trivialized the way they approach your game in your statement, (again, okay, but your elitism is showing) but you haven't invoked your DM authority to clamp down on it whether they, we, or I agree with your decision or not. I in fact stated in my post that
your preference is beyond players' ability to override rules-wise§ (trivial or not). The point being Rule 0 applies
even when it's trivial. No matter. But with that, just like great responsibility coming with great power, so too does the issue of resentment or distaste aimed at you when you are forced to use it to
better your game (in your opinion). Don't take it personally, it's part of the craft.
You (and I'm assuming most of your players) value your concept over a video-game mentality, I happen to agree with you on that for my own RPG time (heck I'd rather be playing B/X!), but I can also get where your friends are coming from. Not being comfortable in making the hard decisions to weed out players who see it differently from you is where you will have to examine your own personal situation and deal with it. That was the crux of the post you quoted -the tough personal choices ahead of you, but you zeroed in on the word trivial†. I hope this follow-up explains where I am coming from at least.
* unless it's the tiny feet, I'm on board with that...
†
edit: on further review with a thesaurus, I'll admit the negative connotation associated with the word is overreaching, but keep in mind I have a personal ax I'm grinding with my own DM when I am typing this, not specifically you. I can't yet find a better substitute. Blame my American education <:-|

‡
quibble: that sliver of historical detail turned mechanical nightmare %$#! is annoying to the point that it kills immersion rather than adds to it. The same is often said of encumbrance but at least that serves important game functions like making STR matter but it's so often handwaved away as inconvenient which facilitates dumping the stat that much easier. YMMV
§ Sort of, I mean by the account you gave they are still breaking your requests, so either you didn't put the true hammer down, or they are balking at the measure, not sure which. Did you lose control of your game or are you still stepping softly with the big stick?