So, in IT my crew and I often use what we call the "shooting gallery" method, which is: "If you can shoot every last bullet you can think of at it and nothing dents it, then the idea AS YOU KNOW IT is sound". Kind of a scientific method thing where you try to break your theory to test if it's a decent theory.
This, I feel, is where the X-card doesn't pass the test.
@faraday hit the nail on the head when she mentioned that the point of the X-card is "no questions asked". This is a key point to the X-card because the method believes that one should not have to justify why they pushed the X-card, and that an immediate detour needs to be made to be inclusive to their wishes.
Here is how the X-card gets a bullet shot in it:
Say you're a tabletop (convention, house game, OTT, even Mush) GM who had written an adventure surrounding a murder investigation.
X-card gets pressed on the word 'murder'
Now...the entire session focused on solving a murder is:
- Not supposed to hash out the details
- is expected to immediately detour, no questions asked
- The topic of said murder (and investigating it) is core to all of the effort the GM put into the session
- The X-card presser expects to not be asked to leave
- The GM has....nofuckingclue what to do
Changeling: The Lost is essentially about kidnapped children who are abused by alien-minded entities.
X-Card on 'kidnap' or mention of Gentry
That's...gonna be rough
Zombie game with high mortality rate and depictions of dead people...
X-card on PC death and descriptions of dead bodies
I could go on, but so long as the expectation is that there are no questions asked and that the table needs to accommodate for said X-card presser's wishes, there's no good way to navigate the pressing of that damn card if they press it on something impassable. If "no questions asked" and "cant ask player to leave" is non-negotiable, then it presents an impasse that "proper adult communication skills" is not subject to.
There is no good "game design" method (other than excluding the player from the game) that exists for "what to do if the player doesn't want to play your story, but still wants to play the game."