The phrase "trust the DM" isn't about trusting them no matter what they do, it's about giving them the benefit of the doubt and don't question every minor decision they make.
Then it should not be used to
excuse behavior that players find troubling.
That is how it has been used. Repeatedly, in this very thread. Indeed, every single time I have brought up a player being concerned about something the DM has said, you and numerous other people have said "wow, sucks you can't just trust people".
If they make decisions you disagree with that you can't talk to them, although for small stuff I think it should be after the game.
Okay. I would say I think it's really important to not take an overly-generous definition of "small stuff" (and yes, I'm pretty much of the opinion that most folks here consider anything short of
outright campaign destruction to be "small stuff"). But if we have a more reasonable definition, e.g. "a single, temporary ruling to get past a logjam 'cause nobody could find it in the book" or "a single weird description that totally failed to effectively communicate what the DM was thinking", then yes, leave small stuff for after the game.
That's why I gave my example of something that
wasn't small stuff--and even then, the player waited and gave the DM a chance to work it out privately, rather than making a big public stink about it. And guess what? I was told that the DM straight-up stonewalling the player, refusing to give any response whatsoever beyond "nope, you
just can't" to a perfectly reasonable course of action, and that the player SHOULD just trust them--regardless of their seemingly very railroad-y behavior.
The scenario in question was a major error, something that may have caused me to leave the game. My advice is to talk to any GM that makes this kind of call before walking out because nobody is perfect. Even if it is unlikely for there to be a resolution. But yes, we have an example here of when trusting your GM gets tossed out the window should really be something like "Trust your GM until proven otherwise and accept that no GM is perfect and there will always be little things you don't agree with. Even if it is something you really disagree with you should try to talk to them because maybe they can learn from their mistake." But that's a bit too long for most people.
Okay. How about what I said before?
In pithy form: Give your GM
allowance, so they have time to
earn your trust. Then, small issues are water under the bridge, and big ones you have a
reason to stick around and listen.
That's the really nice thing about recognizing trust as something that is
built and
earned, not something that is automatic and guaranteed merely by putting on the GM's hat. (I like to think the non-autocratic GM would wear a tricorne as opposed to a "viking hat"--both nautical, but one much more
jaunty than the other.) That is, when trust is something you build rather than something automatic, the player can look back and point at specific times where they were unsure, and the GM came through for them. They can know, from actual lived experience and not a dismissive "you just HAVE to trust me", that the GM actually puts her money where her mouth is, that she goes the distance, that when it
isn't of critical importance she really will work with them to resolve an issue. Rather than taking all of that on total blind faith, rather than presuming that trust comes in two and only two states (perfect or shattered), it recognizes trust as something that grows and changes with time, something that can come in fits and starts or that can be damaged or weakened
and later repaired.